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tcsh - C shell with file name completion and command line editing

 

NAME

        tcsh - C shell with file name completion and command line editing
 

SYNOPSIS

        tcsh [-bcdefFimnqstvVxX] [-Dname[=value]] [arg ...]
        tcsh -l
 

DESCRIPTION

        tcsh  is  an enhanced but completely compatible version of the Berkeley
        UNIX C shell, csh(1).  It is a command language interpreter usable both
        as an interactive login shell and a shell script command processor.  It
        includes a command-line editor  (see  The  command-line  editor),  pro‐
        grammable  word  completion (see Completion and listing), spelling cor‐
        rection (see Spelling correction), a  history  mechanism  (see  History
        substitution),  job  control  (see  Jobs) and a C-like syntax.  The NEW
        FEATURES section describes major  enhancements  of  tcsh  over  csh(1).
        Throughout  this  manual,  features  of  tcsh  not found in most csh(1)
        implementations (specifically, the 4.4BSD csh) are labeled with  ‘(+)’,
        and features which are present in csh(1) but not usually documented are
        labeled with ‘(u)’.
 
    Argument list processing
        If the first argument (argument 0) to the shell is ‘-’  then  it  is  a
        login shell.  A login shell can be also specified by invoking the shell
        with the -l flag as the only argument.
 
        The rest of the flag arguments are interpreted as follows:
 
        -b  Forces a ‘‘break’’ from  option  processing,  causing  any  further
            shell arguments to be treated as non-option arguments.  The remain‐
            ing arguments will not be interpreted as shell options.   This  may
            be used to pass options to a shell script without confusion or pos‐
            sible subterfuge.  The shell will not  run  a  set-user  ID  script
            without this option.
 
        -c  Commands  are  read  from  the  following  argument  (which must be
            present, and must be a single  argument),  stored  in  the  command
            shell  variable  for  reference, and executed.  Any remaining argu‐
            ments are placed in the argv shell variable.
 
        -d  The shell loads the directory stack from  ~/.cshdirs  as  described
            under Startup and shutdown, whether or not it is a login shell. (+)
 
        -Dname[=value]
            Sets the environment variable name to value. (Domain/OS only) (+)
 
        -e  The shell exits if any invoked  command  terminates  abnormally  or
            yields a non-zero exit status.
 
        -f  The shell ignores ~/.tcshrc, and thus starts faster.
 
        -F  The  shell  uses  fork(2)  instead  of vfork(2) to spawn processes.
            (Convex/OS only) (+)
 
        -i  The shell is interactive and prompts for its top-level input,  even
            if it appears to not be a terminal.  Shells are interactive without
            this option if their inputs and outputs are terminals.
 
        -l  The shell is a login shell.  Applicable only if -l is the only flag
            specified.
 
        -m  The  shell loads ~/.tcshrc even if it does not belong to the effec‐
            tive user.  Newer versions of su(1) can pass -m to the shell. (+)
 
        -n  The shell parses commands but does not execute them.  This aids  in
            debugging shell scripts.
 
        -q  The shell accepts SIGQUIT (see Signal handling) and behaves when it
            is used under a debugger.  Job control is disabled. (u)
 
        -s  Command input is taken from the standard input.
 
        -t  The shell reads and executes a single line of input.  A ‘\’ may  be
            used  to  escape  the  newline at the end of this line and continue
            onto another line.
 
        -v  Sets the verbose shell variable, so that command  input  is  echoed
            after history substitution.
 
        -x  Sets  the  echo shell variable, so that commands are echoed immedi‐
            ately before execution.
 
        -V  Sets the verbose shell variable even before executing ~/.tcshrc.
 
        -X  Is to -x as -V is to -v.
 
        After processing of flag arguments, if arguments remain but none of the
        -c,  -i,  -s,  or -t options were given, the first argument is taken as
        the name of a file of commands, or ‘‘script’’,  to  be  executed.   The
        shell opens this file and saves its name for possible resubstitution by
        ‘$0’.  Because many systems use either the standard version 6  or  ver‐
        sion  7  shells whose shell scripts are not compatible with this shell,
        the shell uses such a ‘standard’ shell to execute a script whose  first
        character is not a ‘#’, i.e., that does not start with a comment.
 
        Remaining arguments are placed in the argv shell variable.
 
    Startup and shutdown
        A  login  shell  begins  by  executing  commands  from the system files
        /etc/csh.cshrc and /etc/csh.login.   It  then  executes  commands  from
        files  in  the  user’s  home  directory:  first  ~/.tcshrc  (+)  or, if
        ~/.tcshrc is not found, ~/.cshrc, then ~/.history (or the value of  the
        histfile shell variable), then ~/.login, and finally ~/.cshdirs (or the
        value of  the  dirsfile  shell  variable)  (+).   The  shell  may  read
        /etc/csh.login  before  instead  of  after /etc/csh.cshrc, and ~/.login
        before instead of after ~/.tcshrc or ~/.cshrc  and  ~/.history,  if  so
        compiled; see the version shell variable. (+)
 
        Non-login  shells read only /etc/csh.cshrc and ~/.tcshrc or ~/.cshrc on
        startup.
 
        For examples of startup  files,  please  consult  http://tcshrc.source‐
        forge.net.
 
        Commands  like  stty(1)  and  tset(1),  which need be run only once per
        login, usually go in one’s ~/.login file.  Users who need  to  use  the
        same  set  of  files with both csh(1) and tcsh can have only a ~/.cshrc
        which checks for the existence of the tcsh shell variable (q.v.) before
        using  tcsh-specific  commands,  or  can  have  both  a  ~/.cshrc and a
        ~/.tcshrc which sources (see the builtin command) ~/.cshrc.   The  rest
        of  this manual uses ‘~/.tcshrc’ to mean ‘~/.tcshrc or, if ~/.tcshrc is
        not found, ~/.cshrc’.
 
        In the normal case, the shell begins reading commands from  the  termi‐
        nal,  prompting with ‘> ’.  (Processing of arguments and the use of the
        shell to process files containing command scripts are described later.)
        The  shell  repeatedly  reads  a  line of command input, breaks it into
        words, places it on the command history list, parses  it  and  executes
        each command in the line.
 
        One can log out by typing ‘^D’ on an empty line, ‘logout’ or ‘login’ or
        via the shell’s autologout mechanism (see the  autologout  shell  vari‐
        able).  When a login shell terminates it sets the logout shell variable
        to ‘normal’ or ‘automatic’ as appropriate, then executes commands  from
        the  files  /etc/csh.logout  and  ~/.logout.  The shell may drop DTR on
        logout if so compiled; see the version shell variable.
 
        The names of the system login and logout files vary from system to sys‐
        tem for compatibility with different csh(1) variants; see FILES.
 
    Editing
        We  first describe The command-line editor.  The Completion and listing
        and Spelling correction sections describe  two  sets  of  functionality
        that  are  implemented  as  editor commands but which deserve their own
        treatment.  Finally, Editor commands lists  and  describes  the  editor
        commands specific to the shell and their default bindings.
 
    The command-line editor (+)
        Command-line  input  can  be edited using key sequences much like those
        used in GNU Emacs or vi(1).  The editor is active only  when  the  edit
        shell  variable  is  set, which it is by default in interactive shells.
        The bindkey builtin can display and change key  bindings.   Emacs-style
        key  bindings are used by default (unless the shell was compiled other‐
        wise; see the version shell variable), but bindkey can change  the  key
        bindings to vi-style bindings en masse.
 
        The  shell always binds the arrow keys (as defined in the TERMCAP envi‐
        ronment variable) to
 
            down    down-history
            up      up-history
            left    backward-char
            right   forward-char
 
        unless doing so would alter another single-character binding.  One  can
        set  the  arrow  key escape sequences to the empty string with settc to
        prevent these bindings.  The ANSI/VT100 sequences for  arrow  keys  are
        always bound.
 
        Other  key  bindings are, for the most part, what Emacs and vi(1) users
        would expect and can easily be displayed by bindkey,  so  there  is  no
        need to list them here.  Likewise, bindkey can list the editor commands
        with a short description of each.
 
        Note that editor commands do not have the same notion of a ‘‘word’’  as
        does  the  shell.   The editor delimits words with any non-alphanumeric
        characters not in the shell variable wordchars, while the shell  recog‐
        nizes  only whitespace and some of the characters with special meanings
        to it, listed under Lexical structure.
 
    Completion and listing (+)
        The shell is often able to complete words when given a unique abbrevia‐
        tion.  Type part of a word (for example ‘ls /usr/lost’) and hit the tab
        key to run the complete-word editor command.  The shell  completes  the
        filename  ‘/usr/lost’  to  ‘/usr/lost+found/’, replacing the incomplete
        word with the complete word in the input buffer.   (Note  the  terminal
        ‘/’;  completion  adds  a ‘/’ to the end of completed directories and a
        space to the end of other completed words, to speed typing and  provide
        a visual indicator of successful completion.  The addsuffix shell vari‐
        able can be unset to prevent this.)  If  no  match  is  found  (perhaps
        ‘/usr/lost+found’ doesn’t exist), the terminal bell rings.  If the word
        is already complete (perhaps there is a ‘/usr/lost’ on your system,  or
        perhaps  you  were  thinking too far ahead and typed the whole thing) a
        ‘/’ or space is added to the end if it isn’t already there.
 
        Completion works anywhere in the line, not at just the  end;  completed
        text  pushes  the  rest  of  the  line to the right.  Completion in the
        middle of a word often results in leftover characters to the  right  of
        the cursor that need to be deleted.
 
        Commands  and  variables  can  be  completed in much the same way.  For
        example, typing ‘em[tab]’ would complete ‘em’ to ‘emacs’ if emacs  were
        the  only  command  on your system beginning with ‘em’.  Completion can
        find a command in any directory in path or if given  a  full  pathname.
        Typing  ‘echo  $ar[tab]’  would  complete  ‘$ar’ to ‘$argv’ if no other
        variable began with ‘ar’.
 
        The shell parses the input buffer to determine  whether  the  word  you
        want  to  complete  should be completed as a filename, command or vari‐
        able.  The first word in the buffer and the first word  following  ‘;’,
        ‘|’,  ‘|&’,  ‘&&’ or ‘||’ is considered to be a command.  A word begin‐
        ning with ‘$’ is considered to be a variable.  Anything else is a file‐
        name.  An empty line is ‘completed’ as a filename.
 
        You  can  list the possible completions of a word at any time by typing
        ‘^D’ to run the delete-char-or-list-or-eof editor command.   The  shell
        lists  the  possible  completions  using  the  ls-F builtin (q.v.)  and
        reprints the prompt and unfinished command line, for example:
 
            > ls /usr/l[^D]
            lbin/       lib/        local/      lost+found/
            > ls /usr/l
 
        If the autolist shell variable is set, the shell  lists  the  remaining
        choices (if any) whenever completion fails:
 
            > set autolist
            > nm /usr/lib/libt[tab]
            libtermcap.a@ libtermlib.a@
            > nm /usr/lib/libterm
 
        If autolist is set to ‘ambiguous’, choices are listed only when comple‐
        tion fails and adds no new characters to the word being completed.
 
        A filename to be completed can contain variables, your own  or  others’
        home  directories  abbreviated with ‘~’ (see Filename substitution) and
        directory stack entries abbreviated with ‘=’ (see Directory stack  sub     
        stitution).  For example,
 
            > ls ~k[^D]
            kahn    kas     kellogg
            > ls ~ke[tab]
            > ls ~kellogg/
 
        or
 
            > set local = /usr/local
            > ls $lo[tab]
            > ls $local/[^D]
            bin/ etc/ lib/ man/ src/
            > ls $local/
 
        Note  that  variables  can also be expanded explicitly with the expand-
        variables editor command.
 
        delete-char-or-list-or-eof lists at only the end of the  line;  in  the
        middle  of  a  line it deletes the character under the cursor and on an
        empty line it logs one out or,  if  ignoreeof  is  set,  does  nothing.
        ‘M-^D’, bound to the editor command list-choices, lists completion pos‐
        sibilities anywhere on a line, and list-choices  (or  any  one  of  the
        related  editor  commands that do or don’t delete, list and/or log out,
        listed under delete-char-or-list-or-eof) can be bound to ‘^D’ with  the
        bindkey builtin command if so desired.
 
        The complete-word-fwd and complete-word-back editor commands (not bound
        to any keys by default) can be used to cycle up and  down  through  the
        list  of possible completions, replacing the current word with the next
        or previous word in the list.
 
        The shell variable fignore can be set to  a  list  of  suffixes  to  be
        ignored by completion.  Consider the following:
 
            > ls
            Makefile        condiments.h~   main.o          side.c
            README          main.c          meal            side.o
            condiments.h    main.c~
            > set fignore = (.o \~)
            > emacs ma[^D]
            main.c   main.c~  main.o
            > emacs ma[tab]
            > emacs main.c
 
        ‘main.c~’  and  ‘main.o’  are  ignored by completion (but not listing),
        because they end in suffixes in fignore.  Note that a ‘\’ was needed in
        front  of  ‘~’  to  prevent it from being expanded to home as described
        under Filename substitution.  fignore is ignored if only one completion
        is possible.
 
        If  the  complete  shell  variable  is  set to ‘enhance’, completion 1)
        ignores case and 2) considers periods, hyphens  and  underscores  (‘.’,
        ‘-’  and  ‘_’)  to be word separators and hyphens and underscores to be
        equivalent.  If you had the following files
 
            comp.lang.c      comp.lang.perl   comp.std.c++
            comp.lang.c++    comp.std.c
 
        and typed ‘mail -f c.l.c[tab]’, it  would  be  completed  to  ‘mail  -f
        comp.lang.c’,  and  ^D  would  list  ‘comp.lang.c’ and ‘comp.lang.c++’.
        ‘mail -f c..c++[^D]’ would  list  ‘comp.lang.c++’  and  ‘comp.std.c++’.
        Typing ‘rm a--file[^D]’ in the following directory
 
            A_silly_file    a-hyphenated-file    another_silly_file
 
        would  list  all  three  files, because case is ignored and hyphens and
        underscores are equivalent.  Periods, however, are  not  equivalent  to
        hyphens or underscores.
 
        Completion  and  listing are affected by several other shell variables:
        recexact can be set to complete on the shortest possible unique  match,
        even if more typing might result in a longer match:
 
            > ls
            fodder   foo      food     foonly
            > set recexact
            > rm fo[tab]
 
        just beeps, because ‘fo’ could expand to ‘fod’ or ‘foo’, but if we type
        another ‘o’,
 
            > rm foo[tab]
            > rm foo
 
        the completion completes on ‘foo’, even though ‘food’ and ‘foonly’ also
        match.   autoexpand can be set to run the expand-history editor command
        before each completion attempt, autocorrect can be set to spelling-cor‐
        rect  the  word  to  be completed (see Spelling correction) before each
        completion attempt and correct can be set to complete commands automat‐
        ically  after  one hits ‘return’.  matchbeep can be set to make comple‐
        tion beep or not beep in a variety of situations, and nobeep can be set
        to  never  beep  at  all.   nostat  can be set to a list of directories
        and/or patterns  that  match  directories  to  prevent  the  completion
        mechanism  from  stat(2)ing those directories.  listmax and listmaxrows
        can be set to limit the number of items and  rows  (respectively)  that
        are listed without asking first.  recognize_only_executables can be set
        to make the shell list only executables when listing commands,  but  it
        is quite slow.
 
        Finally, the complete builtin command can be used to tell the shell how
        to complete words other than filenames, commands and  variables.   Com‐
        pletion  and listing do not work on glob-patterns (see Filename substi     
        tution), but the list-glob  and  expand-glob  editor  commands  perform
        equivalent functions for glob-patterns.
 
    Spelling correction (+)
        The shell can sometimes correct the spelling of filenames, commands and
        variable names as well as completing and listing them.
 
        Individual words can be spelling-corrected with the  spell-word  editor
        command (usually bound to M-s and M-S) and the entire input buffer with
        spell-line (usually bound to M-$).  The correct shell variable  can  be
        set to ‘cmd’ to correct the command name or ‘all’ to correct the entire
        line each time return is typed, and autocorrect can be set  to  correct
        the word to be completed before each completion attempt.
 
        When  spelling correction is invoked in any of these ways and the shell
        thinks that any part of the command line is misspelled, it prompts with
        the corrected line:
 
            > set correct = cmd
            > lz /usr/bin
            CORRECT>ls /usr/bin (y|n|e|a)?
 
        One can answer ‘y’ or space to execute the corrected line, ‘e’ to leave
        the uncorrected command in the input buffer, ‘a’ to abort  the  command
        as if ‘^C’ had been hit, and anything else to execute the original line
        unchanged.
 
        Spelling correction recognizes user-defined completions (see  the  com‐
        plete  builtin  command).   If  an input word in a position for which a
        completion is defined resembles a word in the completion list, spelling
        correction  registers  a  misspelling and suggests the latter word as a
        correction.  However, if the input word does not match any of the  pos‐
        sible  completions for that position, spelling correction does not reg‐
        ister a misspelling.
 
        Like completion, spelling correction works anywhere in the line,  push‐
        ing  the rest of the line to the right and possibly leaving extra char‐
        acters to the right of the cursor.
 
        Beware: spelling correction is not  guaranteed  to  work  the  way  one
        intends,  and  is  provided mostly as an experimental feature.  Sugges‐
        tions and improvements are welcome.
 
    Editor commands (+)
        ‘bindkey’ lists  key  bindings  and  ‘bindkey  -l’  lists  and  briefly
        describes  editor  commands.  Only new or especially interesting editor
        commands are described here.  See emacs(1) and vi(1)  for  descriptions
        of each editor’s key bindings.
 
        The  character  or characters to which each command is bound by default
        is given in parentheses.  ‘^character’ means a  control  character  and
        ‘M-character’  a meta character, typed as escape-character on terminals
        without a meta key.  Case counts, but commands that are bound  to  let‐
        ters by default are bound to both lower- and uppercase letters for con‐
        venience.
 
        complete-word (tab)
                Completes a word as described under Completion and listing.
 
        complete-word-back (not bound)
                Like complete-word-fwd, but steps up from the end of the  list.
 
        complete-word-fwd (not bound)
                Replaces  the  current  word with the first word in the list of
                possible completions.  May be repeated to step down through the
                list.   At the end of the list, beeps and reverts to the incom‐
                plete word.
 
        complete-word-raw (^X-tab)
                Like complete-word, but ignores user-defined completions.
 
        copy-prev-word (M-^_)
                Copies the previous word in the current  line  into  the  input
                buffer.  See also insert-last-word.
 
        dabbrev-expand (M-/)
                Expands  the  current word to the most recent preceding one for
                which the current is a leading substring, wrapping  around  the
                history  list  (once)  if  necessary.  Repeating dabbrev-expand
                without any intervening typing changes  to  the  next  previous
                word etc., skipping identical matches much like history-search-
                backward does.
 
        delete-char (not bound)
                Deletes the character under the cursor.  See also  delete-char-
                or-list-or-eof.
 
        delete-char-or-eof (not bound)
                Does  delete-char  if  there is a character under the cursor or
                end-of-file on an empty line.  See also delete-char-or-list-or-
                eof.
 
        delete-char-or-list (not bound)
                Does  delete-char  if  there is a character under the cursor or
                list-choices at the end of the line.  See also  delete-char-or-
                list-or-eof.
 
        delete-char-or-list-or-eof (^D)
                Does  delete-char  if  there  is  a character under the cursor,
                list-choices at the end of the line or end-of-file on an  empty
                line.  See also those three commands, each of which does only a
                single action, and delete-char-or-eof, delete-char-or-list  and
                list-or-eof,  each  of  which  does  a different two out of the
                three.
 
        down-history (down-arrow, ^N)
                Like up-history, but steps down, stopping at the original input
                line.
 
        end-of-file (not bound)
                Signals  an  end  of file, causing the shell to exit unless the
                ignoreeof shell variable (q.v.) is set to  prevent  this.   See
                also delete-char-or-list-or-eof.
 
        expand-history (M-space)
                Expands history substitutions in the current word.  See History
                substitution.  See also magic-space, toggle-literal-history and
                the autoexpand shell variable.
 
        expand-glob (^X-*)
                Expands  the glob-pattern to the left of the cursor.  See File     
                name substitution.
 
        expand-line (not bound)
                Like expand-history, but expands history substitutions in  each
                word in the input buffer,
 
        expand-variables (^X-$)
                Expands  the  variable to the left of the cursor.  See Variable
                substitution.
 
        history-search-backward (M-p, M-P)
                Searches backwards through  the  history  list  for  a  command
                beginning  with  the current contents of the input buffer up to
                the cursor and copies it into the  input  buffer.   The  search
                string  may  be a glob-pattern (see Filename substitution) con‐
                taining ‘*’, ‘?’, ‘[]’ or ‘{}’.   up-history  and  down-history
                will  proceed  from  the appropriate point in the history list.
                Emacs mode only.  See also history-search-forward and i-search-
                back.
 
        history-search-forward (M-n, M-N)
                Like history-search-backward, but searches forward.
 
        i-search-back (not bound)
                Searches  backward  like  history-search-backward,  copies  the
                first match into the input buffer with the cursor positioned at
                the  end of the pattern, and prompts with ‘bck: ’ and the first
                match.  Additional  characters  may  be  typed  to  extend  the
                search,  i-search-back  may be typed to continue searching with
                the same pattern, wrapping around the history  list  if  neces‐
                sary,  (i-search-back  must  be bound to a single character for
                this to work) or one of the following special characters may be
                typed:
 
                    ^W      Appends  the  rest  of the word under the cursor to
                            the search pattern.
                    delete (or any character bound to backward-delete-char)
                            Undoes the effect of the last character  typed  and
                            deletes  a  character  from  the  search pattern if
                            appropriate.
                    ^G      If the previous search was successful,  aborts  the
                            entire  search.  If not, goes back to the last suc‐
                            cessful search.
                    escape  Ends the search, leaving the current  line  in  the
                            input buffer.
 
                Any other character not bound to self-insert-command terminates
                the search, leaving the current line in the input  buffer,  and
                is then interpreted as normal input.  In particular, a carriage
                return causes the current line  to  be  executed.   Emacs  mode
                only.  See also i-search-fwd and history-search-backward.
 
        i-search-fwd (not bound)
                Like i-search-back, but searches forward.
 
        insert-last-word (M-_)
                Inserts  the  last  word of the previous input line (‘!$’) into
                the input buffer.  See also copy-prev-word.
 
        list-choices (M-^D)
                Lists completion possibilities as  described  under  Completion
                and  listing.   See  also  delete-char-or-list-or-eof and list-
                choices-raw.
 
        list-choices-raw (^X-^D)
                Like list-choices, but ignores user-defined completions.
 
        list-glob (^X-g, ^X-G)
                Lists (via the ls-F builtin) matches to the  glob-pattern  (see
                Filename substitution) to the left of the cursor.
 
        list-or-eof (not bound)
                Does  list-choices  or  end-of-file on an empty line.  See also
                delete-char-or-list-or-eof.
 
        magic-space (not bound)
                Expands history substitutions in the current line, like expand-
                history,  and  appends  a space.  magic-space is designed to be
                bound to the space bar, but is not bound by default.
 
        normalize-command (^X-?)
                Searches for the current word in PATH  and,  if  it  is  found,
                replaces  it  with  the  full  path to the executable.  Special
                characters are quoted.  Aliases are  expanded  and  quoted  but
                commands  within  aliases are not.  This command is useful with
                commands that take commands as arguments, e.g., ‘dbx’  and  ‘sh
                -x’.
 
        normalize-path (^X-n, ^X-N)
                Expands  the  current word as described under the ‘expand’ set‐
                ting of the symlinks shell variable.
 
        overwrite-mode (unbound)
                Toggles between input and overwrite modes.
 
        run-fg-editor (M-^Z)
                Saves the current input line and looks for a stopped job with a
                name  equal  to the last component of the file name part of the
                EDITOR or VISUAL environment variables, or, if neither is  set,
                ‘ed’  or  ‘vi’.   If such a job is found, it is restarted as if
                ‘fg %job’ had been typed.  This is  used  to  toggle  back  and
                forth between an editor and the shell easily.  Some people bind
                this command to ‘^Z’ so they can do this even more easily.
 
        run-help (M-h, M-H)
                Searches for documentation on the current  command,  using  the
                same  notion  of  ‘current command’ as the completion routines,
                and prints it.  There is no way to use  a  pager;  run-help  is
                designed  for  short help files.  If the special alias helpcom     
                mand is defined, it is run with the  command  name  as  a  sole
                argument.   Else,  documentation should be in a file named com‐
                mand.help, command.1, command.6, command.8  or  command,  which
                should  be  in one of the directories listed in the HPATH envi‐
                ronment variable.  If there is more than one help file only the
                first is printed.
 
        self-insert-command (text characters)
                In  insert mode (the default), inserts the typed character into
                the input line after the character under the cursor.  In  over‐
                write  mode,  replaces  the character under the cursor with the
                typed character.  The input mode is normally preserved  between
                lines,  but the inputmode shell variable can be set to ‘insert’
                or ‘overwrite’ to put the editor in that mode at the  beginning
                of each line.  See also overwrite-mode.
 
        sequence-lead-in (arrow prefix, meta prefix, ^X)
                Indicates that the following characters are part of a multi-key
                sequence.  Binding a command to  a  multi-key  sequence  really
                creates  two  bindings: the first character to sequence-lead-in
                and the whole sequence to the command.  All sequences beginning
                with  a  character  bound  to  sequence-lead-in are effectively
                bound to undefined-key unless bound to another command.
 
        spell-line (M-$)
                Attempts to correct the spelling of  each  word  in  the  input
                buffer,  like spell-word, but ignores words whose first charac‐
                ter is one of ‘-’, ‘!’, ‘^’ or ‘%’, or which contain  ‘\’,  ‘*’
                or  ‘?’, to avoid problems with switches, substitutions and the
                like.  See Spelling correction.
 
        spell-word (M-s, M-S)
                Attempts to  correct  the  spelling  of  the  current  word  as
                described  under Spelling correction.  Checks each component of
                a word which appears to be a pathname.
 
        toggle-literal-history (M-r, M-R)
                Expands or  ‘unexpands’  history  substitutions  in  the  input
                buffer.  See also expand-history and the autoexpand shell vari‐
                able.
 
        undefined-key (any unbound key)
                Beeps.
 
        up-history (up-arrow, ^P)
                Copies the previous entry in the history list  into  the  input
                buffer.  If histlit is set, uses the literal form of the entry.
                May be repeated to step up through the history  list,  stopping
                at the top.
 
        vi-search-back (?)
                Prompts  with ‘?’ for a search string (which may be a glob-pat‐
                tern, as with history-search-backward),  searches  for  it  and
                copies it into the input buffer.  The bell rings if no match is
                found.  Hitting return ends the  search  and  leaves  the  last
                match  in the input buffer.  Hitting escape ends the search and
                executes the match.  vi mode only.
 
        vi-search-fwd (/)
                Like vi-search-back, but searches forward.
 
        which-command (M-?)
                Does a which (see the description of the  builtin  command)  on
                the first word of the input buffer.
 
    Lexical structure
        The  shell  splits input lines into words at blanks and tabs.  The spe‐
        cial characters ‘&’, ‘|’, ‘;’, ‘<’, ‘>’, ‘(’, and ‘)’ and  the  doubled
        characters ‘&&’, ‘||’, ‘<<’ and ‘>>’ are always separate words, whether
        or not they are surrounded by whitespace.
 
        When the shell’s input is not a terminal, the character ‘#’ is taken to
        begin  a  comment.  Each ‘#’ and the rest of the input line on which it
        appears is discarded before further parsing.
 
        A special character (including a blank or tab) may  be  prevented  from
        having  its special meaning, and possibly made part of another word, by
        preceding it with a backslash (‘\’) or enclosing it  in  single  (‘’’),
        double  (‘"’)  or  backward  (‘‘’) quotes.  When not otherwise quoted a
        newline preceded by a ‘\’ is equivalent to a blank, but  inside  quotes
        this sequence results in a newline.
 
        Furthermore,  all Substitutions (see below) except History substitution
        can be prevented by enclosing the strings  (or  parts  of  strings)  in
        which  they appear with single quotes or by quoting the crucial charac‐
        ter(s) (e.g., ‘$’ or ‘‘’ for Variable substitution or Command substitu     
        tion  respectively)  with  ‘\’.   (Alias  substitution is no exception:
        quoting in any way any character of a word for which an alias has  been
        defined  prevents  substitution of the alias.  The usual way of quoting
        an alias is to precede it with a backslash.)  History  substitution  is
        prevented by backslashes but not by single quotes.  Strings quoted with
        double or backward quotes undergo  Variable  substitution  and  Command
        substitution, but other substitutions are prevented.
 
        Text  inside  single or double quotes becomes a single word (or part of
        one).  Metacharacters in these strings, including blanks and  tabs,  do
        not form separate words.  Only in one special case (see Command substi     
        tution below) can a double-quoted string yield parts of more  than  one
        word;  single-quoted  strings  never  do.  Backward quotes are special:
        they signal Command substitution (q.v.), which may result in more  than
        one word.
 
        Quoting  complex strings, particularly strings which themselves contain
        quoting characters, can be confusing.  Remember that quotes need not be
        used  as  they  are in human writing!  It may be easier to quote not an
        entire string, but only those parts of the string which  need  quoting,
        using different types of quoting to do so if appropriate.
 
        The  backslash_quote  shell  variable  (q.v.)  can be set to make back‐
        slashes always quote ‘\’, ‘’’, and ‘"’.   (+)  This  may  make  complex
        quoting tasks easier, but it can cause syntax errors in csh(1) scripts.
 
    Substitutions
        We now describe the various transformations the shell performs  on  the
        input  in  the  order in which they occur.  We note in passing the data
        structures involved and the commands and variables which  affect  them.
        Remember  that  substitutions  can be prevented by quoting as described
        under Lexical structure.
 
    History substitution
        Each command, or ‘‘event’’, input from the terminal  is  saved  in  the
        history  list.   The  previous command is always saved, and the history
        shell variable can be set to a number to save that many commands.   The
        histdup  shell variable can be set to not save duplicate events or con‐
        secutive duplicate events.
 
        Saved commands are numbered sequentially from 1 and  stamped  with  the
        time.   It  is not usually necessary to use event numbers, but the cur‐
        rent event number can be made part of the prompt by placing an  ‘!’  in
        the prompt shell variable.
 
        The  shell  actually saves history in expanded and literal (unexpanded)
        forms.  If the histlit shell variable is set, commands that display and
        store history use the literal form.
 
        The  history  builtin  command  can print, store in a file, restore and
        clear the history list at any time, and the savehist and histfile shell
        variables  can be can be set to store the history list automatically on
        logout and restore it on login.
 
        History substitutions introduce words from the history  list  into  the
        input  stream, making it easy to repeat commands, repeat arguments of a
        previous command in the current command, or fix  spelling  mistakes  in
        the  previous  command  with  little typing and a high degree of confi‐
        dence.
 
        History substitutions begin with the character  ‘!’.   They  may  begin
        anywhere  in  the  input  stream, but they do not nest.  The ‘!’ may be
        preceded by a ‘\’ to prevent its special meaning;  for  convenience,  a
        ‘!’  is  passed unchanged when it is followed by a blank, tab, newline,
        ‘=’ or ‘(’.  History substitutions also occur when an input line begins
        with  ‘^’.   This  special  abbreviation  will be described later.  The
        characters used to signal history substitution (‘!’  and  ‘^’)  can  be
        changed  by setting the histchars shell variable.  Any input line which
        contains a history substitution is printed before it is executed.
 
        A history substitution may have an ‘‘event specification’’, which indi‐
        cates  the  event  from  which words are to be taken, a ‘‘word designa‐
        tor’’, which selects particular words from the chosen event,  and/or  a
        ‘‘modifier’’, which manipulates the selected words.
 
        An event specification can be
 
            n       A number, referring to a particular event
            -n      An  offset,  referring  to  the  event n before the current
                    event
            #       The current  event.   This  should  be  used  carefully  in
                    csh(1), where there is no check for recursion.  tcsh allows
                    10 levels of recursion.  (+)
            !       The previous event (equivalent to ‘-1’)
            s       The most recent event whose  first  word  begins  with  the
                    string s
            ?s?     The  most  recent  event  which contains the string s.  The
                    second ‘?’ can be omitted if it is immediately followed  by
                    a newline.
 
        For example, consider this bit of someone’s history list:
 
             9  8:30    nroff -man wumpus.man
            10  8:31    cp wumpus.man wumpus.man.old
            11  8:36    vi wumpus.man
            12  8:37    diff wumpus.man.old wumpus.man
 
        The  commands  are shown with their event numbers and time stamps.  The
        current event, which we haven’t typed in yet, is event 13.   ‘!11’  and
        ‘!-2’  refer to event 11.  ‘!!’ refers to the previous event, 12.  ‘!!’
        can be abbreviated ‘!’ if it is  followed  by  ‘:’  (‘:’  is  described
        below).   ‘!n’ refers to event 9, which begins with ‘n’.  ‘!?old?’ also
        refers to event 12, which contains ‘old’.  Without word designators  or
        modifiers  history  references simply expand to the entire event, so we
        might type ‘!cp’ to redo the copy command or ‘!!|more’  if  the  ‘diff’
        output scrolled off the top of the screen.
 
        History  references  may  be  insulated  from the surrounding text with
        braces if necessary.  For example, ‘!vdoc’ would  look  for  a  command
        beginning  with  ‘vdoc’,  and,  in  this  example,  not  find  one, but
        ‘!{v}doc’ would expand unambiguously to ‘vi  wumpus.mandoc’.   Even  in
        braces, history substitutions do not nest.
 
        (+) While csh(1) expands, for example, ‘!3d’ to event 3 with the letter
        ‘d’ appended to it, tcsh expands it to the last  event  beginning  with
        ‘3d’;  only  completely numeric arguments are treated as event numbers.
        This makes it possible to recall events  beginning  with  numbers.   To
        expand ‘!3d’ as in csh(1) say ‘!\3d’.
 
        To  select words from an event we can follow the event specification by
        a ‘:’ and a designator for the desired words.  The words  of  an  input
        line are numbered from 0, the first (usually command) word being 0, the
        second word (first argument) being 1, etc.  The basic word  designators
        are:
 
            0       The first (command) word
            n       The nth argument
            ^       The first argument, equivalent to ‘1’
            $       The last argument
            %       The word matched by an ?s? search
            x-y     A range of words
            -y      Equivalent to ‘0-y’
            *       Equivalent  to ‘^-$’, but returns nothing if the event con‐
                    tains only 1 word
            x*      Equivalent to ‘x-$’
            x-      Equivalent to ‘x*’, but omitting the last word (‘$’)
 
        Selected words are inserted into the command line separated  by  single
        blanks.   For example, the ‘diff’ command in the previous example might
        have been typed as ‘diff !!:1.old !!:1’ (using ‘:1’ to select the first
        argument  from  the previous event) or ‘diff !-2:2 !-2:1’ to select and
        swap the arguments from the ‘cp’ command.  If we didn’t care about  the
        order  of  the ‘diff’ we might have said ‘diff !-2:1-2’ or simply ‘diff
        !-2:*’.  The ‘cp’  command  might  have  been  written  ‘cp  wumpus.man
        !#:1.old’,  using ‘#’ to refer to the current event.  ‘!n:- hurkle.man’
        would reuse the first two words from the ‘nroff’ command to say  ‘nroff
        -man hurkle.man’.
 
        The ‘:’ separating the event specification from the word designator can
        be omitted if the argument selector begins with a ‘^’, ‘$’, ‘*’, ‘%’ or
        ‘-’.   For  example,  our  ‘diff’ command might have been ‘diff !!^.old
        !!^’ or, equivalently, ‘diff !!$.old !!$’.  However, if ‘!!’ is  abbre‐
        viated ‘!’, an argument selector beginning with ‘-’ will be interpreted
        as an event specification.
 
        A history reference may have a word designator but no event  specifica‐
        tion.   It then references the previous command.  Continuing our ‘diff’
        example, we could have said simply ‘diff !^.old  !^’  or,  to  get  the
        arguments in the opposite order, just ‘diff !*’.
 
        The  word  or  words  in  a history reference can be edited, or ‘‘modi‐
        fied’’, by following it with one or more modifiers, each preceded by  a
        ‘:’:
 
            h       Remove a trailing pathname component, leaving the head.
            t       Remove all leading pathname components, leaving the tail.
            r       Remove  a filename extension ‘.xxx’, leaving the root name.
            e       Remove all but the extension.
            u       Uppercase the first lowercase letter.
            l       Lowercase the first uppercase letter.
            s/l/r/  Substitute l for r.  l is simply a string  like  r,  not  a
                    regular  expression as in the eponymous ed(1) command.  Any
                    character may be used as the delimiter in place of  ‘/’;  a
                    ‘\’ can be used to quote the delimiter inside l and r.  The
                    character ‘&’ in the r is replaced by l;  ‘\’  also  quotes
                    ‘&’.  If l is empty (‘‘’’), the l from a previous substitu‐
                    tion or the s from a previous ‘?s?’ event specification  is
                    used.  The trailing delimiter may be omitted if it is imme‐
                    diately followed by a newline.
            &       Repeat the previous substitution.
            g       Apply the following modifier once to each word.
            a (+)   Apply the following modifier as many times as possible to a
                    single  word.   ‘a’ and ‘g’ can be used together to apply a
                    modifier globally.  In the  current  implementation,  using
                    the  ‘a’ and ‘s’ modifiers together can lead to an infinite
                    loop.  For example, ‘:as/f/ff/’ will never terminate.  This
                    behavior might change in the future.
            p       Print the new command line but do not execute it.
            q       Quote  the  substituted words, preventing further substitu‐
                    tions.
            x       Like q, but break into words at blanks, tabs and  newlines.
 
        Modifiers  are applied to only the first modifiable word (unless ‘g’ is
        used).  It is an error for no word to be modifiable.
 
        For example, the ‘diff’ command might have been written as  ‘diff  wum‐
        pus.man.old !#^:r’, using ‘:r’ to remove ‘.old’ from the first argument
        on the same line (‘!#^’).  We could say ‘echo hello  out  there’,  then
        ‘echo  !*:u’ to capitalize ‘hello’, ‘echo !*:au’ to say it out loud, or
        ‘echo !*:agu’ to really shout.  We might follow ‘mail -s "I  forgot  my
        password"  rot’  with  ‘!:s/rot/root’ to correct the spelling of ‘root’
        (but see Spelling correction for a different approach).
 
        There is a special abbreviation for substitutions.  ‘^’, when it is the
        first  character  on  an  input line, is equivalent to ‘!:s^’.  Thus we
        might have said ‘^rot^root’ to make the spelling correction in the pre‐
        vious  example.   This  is the only history substitution which does not
        explicitly begin with ‘!’.
 
        (+) In csh as such, only one modifier may be applied to each history or
        variable expansion.  In tcsh, more than one may be used, for example
 
            % mv wumpus.man /usr/man/man1/wumpus.1
            % man !$:t:r
            man wumpus
 
        In csh, the result would be ‘wumpus.1:r’.  A substitution followed by a
        colon may need to be insulated from it with braces:
 
            > mv a.out /usr/games/wumpus
            > setenv PATH !$:h:$PATH
            Bad ! modifier: $.
            > setenv PATH !{-2$:h}:$PATH
            setenv PATH /usr/games:/bin:/usr/bin:.
 
        The first attempt would succeed in csh but fails in tcsh, because  tcsh
        expects another modifier after the second colon rather than ‘$’.
 
        Finally,  history can be accessed through the editor as well as through
        the substitutions just described.  The up- and  down-history,  history-
        search-backward  and  -forward,  i-search-back and -fwd, vi-search-back
        and -fwd, copy-prev-word and insert-last-word  editor  commands  search
        for  events  in  the  history list and copy them into the input buffer.
        The toggle-literal-history editor command switches between the expanded
        and literal forms of history lines in the input buffer.  expand-history
        and expand-line expand history substitutions in the current word and in
        the entire input buffer respectively.
 
    Alias substitution
        The  shell  maintains  a  list  of  aliases which can be set, unset and
        printed by the alias and unalias commands.  After  a  command  line  is
        parsed  into simple commands (see Commands) the first word of each com‐
        mand, left-to-right, is checked to see if it has an alias.  If so,  the
        first  word  is replaced by the alias.  If the alias contains a history
        reference, it undergoes History substitution (q.v.) as though the orig‐
        inal  command were the previous input line.  If the alias does not con‐
        tain a history reference, the argument list is left untouched.
 
        Thus if the alias for ‘ls’ were ‘ls -l’ the  command  ‘ls  /usr’  would
        become  ‘ls -l /usr’, the argument list here being undisturbed.  If the
        alias for ‘lookup’ were ‘grep !^ /etc/passwd’ then ‘lookup bill’  would
        become  ‘grep  bill  /etc/passwd’.   Aliases  can  be used to introduce
        parser metasyntax.  For example, ‘alias print ’pr \!* | lpr’’ defines a
        ‘‘command’’ (‘print’) which pr(1)s its arguments to the line printer.
 
        Alias  substitution is repeated until the first word of the command has
        no alias.  If an alias substitution does not change the first word  (as
        in  the previous example) it is flagged to prevent a loop.  Other loops
        are detected and cause an error.
 
        Some aliases are referred to by the shell; see Special aliases.
 
    Variable substitution
        The shell maintains a list of variables, each of which has as  value  a
        list  of zero or more words.  The values of shell variables can be dis‐
        played and changed with the set and unset commands.  The  system  main‐
        tains  its  own  list  of ‘‘environment’’ variables.  These can be dis‐
        played and changed with printenv, setenv and unsetenv.
 
        (+) Variables may be made read-only with  ‘set  -r’  (q.v.)   Read-only
        variables  may not be modified or unset; attempting to do so will cause
        an error.  Once made read-only, a variable cannot be made writable,  so
        ‘set  -r’ should be used with caution.  Environment variables cannot be
        made read-only.
 
        Some variables are set  by  the  shell  or  referred  to  by  it.   For
        instance,  the  argv variable is an image of the shell’s argument list,
        and words of this variable’s value are referred  to  in  special  ways.
        Some  of  the variables referred to by the shell are toggles; the shell
        does not care what their value is, only whether they are  set  or  not.
        For  instance,  the  verbose  variable is a toggle which causes command
        input to be echoed.  The -v command line  option  sets  this  variable.
        Special  shell  variables  lists all variables which are referred to by
        the shell.
 
        Other operations treat variables numerically.  The ‘@’ command  permits
        numeric calculations to be performed and the result assigned to a vari‐
        able.  Variable values are, however, always  represented  as  (zero  or
        more) strings.  For the purposes of numeric operations, the null string
        is considered to be zero, and the second and subsequent words of multi-
        word values are ignored.
 
        After  the input line is aliased and parsed, and before each command is
        executed, variable substitution is performed keyed by  ‘$’  characters.
        This  expansion can be prevented by preceding the ‘$’ with a ‘\’ except
        within ‘"’s where it always occurs, and  within  ‘’’s  where  it  never
        occurs.   Strings quoted by ‘‘’ are interpreted later (see Command sub     
        stitution below) so ‘$’ substitution does not occur there until  later,
        if  at  all.  A ‘$’ is passed unchanged if followed by a blank, tab, or
        end-of-line.
 
        Input/output redirections are recognized before variable expansion, and
        are  variable  expanded  separately.   Otherwise,  the command name and
        entire argument list are expanded together.  It is  thus  possible  for
        the  first  (command)  word  (to  this point) to generate more than one
        word, the first of which becomes the command  name,  and  the  rest  of
        which become arguments.
 
        Unless  enclosed in ‘"’ or given the ‘:q’ modifier the results of vari‐
        able substitution may eventually be command and  filename  substituted.
        Within  ‘"’,  a variable whose value consists of multiple words expands
        to a (portion of a) single word, with the words of the variable’s value
        separated  by blanks.  When the ‘:q’ modifier is applied to a substitu‐
        tion the variable will expand to multiple words with  each  word  sepa‐
        rated  by  a blank and quoted to prevent later command or filename sub‐
        stitution.
 
        The following metasequences are provided for introducing variable  val‐
        ues into the shell input.  Except as noted, it is an error to reference
        a variable which is not set.
 
        $name
        ${name} Substitutes the words of the value of variable name, each sepa‐
                rated  by a blank.  Braces insulate name from following charac‐
                ters which would otherwise be part of it.  Shell variables have
                names consisting of up to 20 letters and digits starting with a
                letter.  The underscore character is considered a  letter.   If
                name  is  not  a shell variable, but is set in the environment,
                then that value is returned (but ‘:’ modifiers  and  the  other
                forms given below are not available in this case).
        $name[selector]
        ${name[selector]}
                Substitutes  only  the  selected  words from the value of name.
                The selector is subjected to ‘$’ substitution and  may  consist
                of  a  single  number  or  two numbers separated by a ‘-’.  The
                first word of a variable’s value is numbered ‘1’.  If the first
                number  of  a range is omitted it defaults to ‘1’.  If the last
                member of a range is omitted  it  defaults  to  ‘$#name’.   The
                selector ‘*’ selects all words.  It is not an error for a range
                to be empty if the second argument is omitted or in range.
        $0      Substitutes the name of the file from which  command  input  is
                being read.  An error occurs if the name is not known.
        $number
        ${number}
                Equivalent to ‘$argv[number]’.
        $*      Equivalent to ‘$argv’, which is equivalent to ‘$argv[*]’.
 
        The  ‘:’  modifiers  described  under  History substitution, except for
        ‘:p’, can be applied to the substitutions above.  More than one may  be
        used.   (+)  Braces  may  be needed to insulate a variable substitution
        from a literal colon just as with History substitution (q.v.); any mod‐
        ifiers must appear within the braces.
 
        The following substitutions can not be modified with ‘:’ modifiers.
 
        $?name
        ${?name}
                Substitutes the string ‘1’ if name is set, ‘0’ if it is not.
        $?0     Substitutes  ‘1’ if the current input filename is known, ‘0’ if
                it is not.  Always ‘0’ in interactive shells.
        $#name
        ${#name}
                Substitutes the number of words in name.
        $#      Equivalent to ‘$#argv’.  (+)
        $%name
        ${%name}
                Substitutes the number of characters in name.  (+)
        $%number
        ${%number}
                Substitutes the number of characters in $argv[number].  (+)
        $?      Equivalent to ‘$status’.  (+)
        $$      Substitutes the (decimal) process number of the (parent) shell.
        $!      Substitutes the (decimal) process number of the last background
                process started by this shell.  (+)
        $_      Substitutes the command line of the last command executed.  (+)
        $<      Substitutes  a  line  from  the standard input, with no further
                interpretation thereafter.  It can be used  to  read  from  the
                keyboard in a shell script.  (+) While csh always quotes $<, as
                if it were equivalent to ‘$<:q’, tcsh does  not.   Furthermore,
                when  tcsh  is waiting for a line to be typed the user may type
                an interrupt to interrupt the sequence into which the  line  is
                to be substituted, but csh does not allow this.
 
        The  editor  command expand-variables, normally bound to ‘^X-$’, can be
        used to interactively expand individual variables.
 
    Command, filename and directory stack substitution
        The remaining substitutions are applied selectively to the arguments of
        builtin  commands.   This  means that portions of expressions which are
        not evaluated are not subjected  to  these  expansions.   For  commands
        which  are  not  internal to the shell, the command name is substituted
        separately from the argument list.  This occurs very late, after input-
        output redirection is performed, and in a child of the main shell.
 
    Command substitution
        Command  substitution  is  indicated by a command enclosed in ‘‘’.  The
        output from such a command is broken into  separate  words  at  blanks,
        tabs  and  newlines, and null words are discarded.  The output is vari‐
        able and command substituted and put in place of the original string.
 
        Command substitutions inside double  quotes  (‘"’)  retain  blanks  and
        tabs; only newlines force new words.  The single final newline does not
        force a new word in any case.  It is thus possible for a  command  sub‐
        stitution  to  yield only part of a word, even if the command outputs a
        complete line.
 
    Filename substitution
        If a word contains any of the characters ‘*’, ‘?’, ‘[’ or ‘{’ or begins
        with  the  character  ‘~’  it is a candidate for filename substitution,
        also known as ‘‘globbing’’.  This word is then regarded  as  a  pattern
        (‘‘glob-pattern’’),  and replaced with an alphabetically sorted list of
        file names which match the pattern.
 
        In matching filenames, the character ‘.’ at the beginning of a filename
        or  immediately  following  a ‘/’, as well as the character ‘/’ must be
        matched explicitly.  The character ‘*’ matches any  string  of  charac‐
        ters,  including the null string.  The character ‘?’ matches any single
        character.  The sequence ‘[...]’ matches  any  one  of  the  characters
        enclosed.   Within  ‘[...]’,  a  pair  of  characters  separated by ‘-’
        matches any character lexically between the two.
 
        (+) Some glob-patterns can be negated: The  sequence  ‘[^...]’  matches
        any  single  character not specified by the characters and/or ranges of
        characters in the braces.
 
        An entire glob-pattern can also be negated with ‘^’:
 
            > echo *
            bang crash crunch ouch
            > echo ^cr*
            bang ouch
 
        Glob-patterns which do not use ‘?’, ‘*’, or ‘[]’ or which use  ‘{}’  or
        ‘~’ (below) are not negated correctly.
 
        The  metanotation  ‘a{b,c,d}e’ is a shorthand for ‘abe ace ade’.  Left-
        to-right order is preserved: ‘/usr/source/s1/{oldls,ls}.c’  expands  to
        ‘/usr/source/s1/oldls.c  /usr/source/s1/ls.c’.   The results of matches
        are  sorted  separately  at  a  low  level  to  preserve  this   order:
        ‘../{memo,*box}’  might expand to ‘../memo ../box ../mbox’.  (Note that
        ‘memo’ was not sorted with the results of matching ‘*box’.)  It is  not
        an  error  when this construct expands to files which do not exist, but
        it is possible to get an error from a command  to  which  the  expanded
        list  is  passed.  This construct may be nested.  As a special case the
        words ‘{’, ‘}’ and ‘{}’ are passed undisturbed.
 
        The character ‘~’ at the beginning of a filename refers to home  direc‐
        tories.   Standing  alone,  i.e., ‘~’, it expands to the invoker’s home
        directory as reflected in the value of the home shell  variable.   When
        followed by a name consisting of letters, digits and ‘-’ characters the
        shell searches for a user with that name  and  substitutes  their  home
        directory;  thus ‘~ken’ might expand to ‘/usr/ken’ and ‘~ken/chmach’ to
        ‘/usr/ken/chmach’.  If the character ‘~’ is  followed  by  a  character
        other  than  a letter or ‘/’ or appears elsewhere than at the beginning
        of a word, it is left undisturbed.   A  command  like  ‘setenv  MANPATH
        /usr/man:/usr/local/man:~/lib/man’  does not, therefore, do home direc‐
        tory substitution as one might hope.
 
        It is an error for a glob-pattern containing ‘*’, ‘?’, ‘[’ or ‘~’, with
        or without ‘^’, not to match any files.  However, only one pattern in a
        list of glob-patterns must match a file (so that,  e.g.,  ‘rm  *.a  *.c
        *.o’  would  fail  only if there were no files in the current directory
        ending in ‘.a’, ‘.c’, or ‘.o’), and if the nonomatch shell variable  is
        set  a  pattern  (or  list  of  patterns) which matches nothing is left
        unchanged rather than causing an error.
 
        The noglob shell variable can be set to prevent filename  substitution,
        and  the  expand-glob  editor command, normally bound to ‘^X-*’, can be
        used to interactively expand individual filename substitutions.
 
    Directory stack substitution (+)
        The directory stack is a list of directories, numbered from zero,  used
        by  the  pushd, popd and dirs builtin commands (q.v.).  dirs can print,
        store in a file, restore and clear the directory stack at any time, and
        the  savedirs  and  dirsfile  shell  variables  can be set to store the
        directory stack automatically on logout and restore it on  login.   The
        dirstack  shell variable can be examined to see the directory stack and
        set to put arbitrary directories into the directory stack.
 
        The character ‘=’ followed by one or more digits expands to an entry in
        the  directory stack.  The special case ‘=-’ expands to the last direc‐
        tory in the stack.  For example,
 
            > dirs -v
            0       /usr/bin
            1       /usr/spool/uucp
            2       /usr/accts/sys
            > echo =1
            /usr/spool/uucp
            > echo =0/calendar
            /usr/bin/calendar
            > echo =-
            /usr/accts/sys
 
        The noglob and nonomatch shell variables  and  the  expand-glob  editor
        command apply to directory stack as well as filename substitutions.
 
    Other substitutions (+)
        There   are  several  more  transformations  involving  filenames,  not
        strictly related to the above but mentioned here for completeness.  Any
        filename  may  be  expanded  to  a full path when the symlinks variable
        (q.v.) is set to ‘expand’.  Quoting prevents this  expansion,  and  the
        normalize-path editor command does it on demand.  The normalize-command
        editor command expands commands in PATH  into  full  paths  on  demand.
        Finally,  cd  and  pushd  interpret  ‘-’  as  the old working directory
        (equivalent to the shell variable owd).  This is not a substitution  at
        all,  but  an abbreviation recognized by only those commands.  Nonethe‐
        less, it too can be prevented by quoting.
 
    Commands
        The next three sections describe how the shell  executes  commands  and
        deals with their input and output.
 
    Simple commands, pipelines and sequences
        A  simple  command is a sequence of words, the first of which specifies
        the command to be executed.  A series of simple commands joined by  ‘|’
        characters  forms a pipeline.  The output of each command in a pipeline
        is connected to the input of the next.
 
        Simple commands and pipelines may be joined into  sequences  with  ‘;’,
        and  will be executed sequentially.  Commands and pipelines can also be
        joined into sequences with ‘||’ or ‘&&’, indicating, as in the  C  lan‐
        guage,  that  the  second  is to be executed only if the first fails or
        succeeds respectively.
 
        A simple command, pipeline or sequence may be  placed  in  parentheses,
        ‘()’,  to  form a simple command, which may in turn be a component of a
        pipeline or sequence.  A command, pipeline or sequence can be  executed
        without waiting for it to terminate by following it with an ‘&’.
 
    Builtin and non-builtin command execution
        Builtin  commands are executed within the shell.  If any component of a
        pipeline except the last is a builtin command, the pipeline is executed
        in a subshell.
 
        Parenthesized commands are always executed in a subshell.
 
            (cd; pwd); pwd
 
        thus  prints  the  home directory, leaving you where you were (printing
        this after the home directory), while
 
            cd; pwd
 
        leaves you in the home  directory.   Parenthesized  commands  are  most
        often used to prevent cd from affecting the current shell.
 
        When  a command to be executed is found not to be a builtin command the
        shell attempts to execute the command via execve(2).  Each word in  the
        variable  path  names  a directory in which the shell will look for the
        command.  If it is given neither a -c nor a -t option, the shell hashes
        the  names  in these directories into an internal table so that it will
        try an execve(2) in only a directory where there is a possibility  that
        the command resides there.  This greatly speeds command location when a
        large number of directories are present in the search  path.   If  this
        mechanism has been turned off (via unhash), if the shell was given a -c
        or -t argument or in any case for  each  directory  component  of  path
        which  does  not  begin  with a ‘/’, the shell concatenates the current
        working directory with the given command name to form a path name of  a
        file which it then attempts to execute.
 
        If  the  file  has  execute permissions but is not an executable to the
        system (i.e., it is neither an executable  binary  nor  a  script  that
        specifies  its interpreter), then it is assumed to be a file containing
        shell commands and a new shell is spawned to read it.  The  shell  spe‐
        cial  alias  may  be set to specify an interpreter other than the shell
        itself.
 
        On systems which do not understand the ‘#!’ script interpreter  conven‐
        tion  the  shell  may  be compiled to emulate it; see the version shell
        variable.  If so, the shell checks the first line of the file to see if
        it  is of the form ‘#!interpreter arg ...’.  If it is, the shell starts
        interpreter with the given args and feeds the file to  it  on  standard
        input.
 
    Input/output
        The  standard  input and standard output of a command may be redirected
        with the following syntax:
 
        < name  Open file name (which is first variable, command  and  filename
                expanded) as the standard input.
        << word Read  the  shell input up to a line which is identical to word.
                word is not subjected to variable, filename or command  substi‐
                tution, and each input line is compared to word before any sub‐
                stitutions are done on this input line.  Unless a quoting  ‘\’,
                ‘"’,  ‘’  or ‘‘’ appears in word variable and command substitu‐
                tion is performed on the intervening  lines,  allowing  ‘\’  to
                quote  ‘$’,  ‘\’  and ‘‘’.  Commands which are substituted have
                all blanks, tabs, and newlines preserved, except for the  final
                newline  which  is dropped.  The resultant text is placed in an
                anonymous temporary file which is given to the command as stan‐
                dard input.
        > name
        >! name
        >& name
        >&! name
                The file name is used as standard output.  If the file does not
                exist then it is created; if the file exists, it is  truncated,
                its previous contents being lost.
 
                If  the shell variable noclobber is set, then the file must not
                exist or be a character  special  file  (e.g.,  a  terminal  or
                ‘/dev/null’)  or an error results.  This helps prevent acciden‐
                tal destruction of files.  In this case the ‘!’  forms  can  be
                used to suppress this check.
 
                The  forms  involving  ‘&’ route the diagnostic output into the
                specified file  as  well  as  the  standard  output.   name  is
                expanded in the same way as ‘<’ input filenames are.
        >> name
        >>& name
        >>! name
        >>&! name
                Like  ‘>’, but appends output to the end of name.  If the shell
                variable noclobber is set, then it is an error for the file not
                to exist, unless one of the ‘!’ forms is given.
 
        A  command  receives  the environment in which the shell was invoked as
        modified by the input-output parameters and the presence of the command
        in  a pipeline.  Thus, unlike some previous shells, commands run from a
        file of shell commands have no access to the text of  the  commands  by
        default;  rather they receive the original standard input of the shell.
        The ‘<<’ mechanism should be used to present inline data.  This permits
        shell command scripts to function as components of pipelines and allows
        the shell to block read its input.   Note  that  the  default  standard
        input  for  a command run detached is not the empty file /dev/null, but
        the original standard input of the shell.  If this is a terminal and if
        the  process  attempts to read from the terminal, then the process will
        block and the user will be notified (see Jobs).
 
        Diagnostic output may be directed through a pipe with the standard out‐
        put.  Simply use the form ‘|&’ rather than just ‘|’.
 
        The  shell  cannot  presently  redirect  diagnostic output without also
        redirecting standard output, but ‘(command  >  output-file)  >&  error-
        file’  is often an acceptable workaround.  Either output-file or error-
        file may be ‘/dev/tty’ to send output to the terminal.
 
    Features
        Having described how the shell accepts,  parses  and  executes  command
        lines, we now turn to a variety of its useful features.
 
    Control flow
        The  shell  contains a number of commands which can be used to regulate
        the flow of control in command files (shell scripts)  and  (in  limited
        but  useful  ways)  from terminal input.  These commands all operate by
        forcing the shell to reread or skip in its input and, due to the imple‐
        mentation, restrict the placement of some of the commands.
 
        The  foreach, switch, and while statements, as well as the if-then-else
        form of the if statement, require that the major keywords appear  in  a
        single simple command on an input line as shown below.
 
        If  the shell’s input is not seekable, the shell buffers up input when‐
        ever a loop is being read and performs seeks in this internal buffer to
        accomplish the rereading implied by the loop.  (To the extent that this
        allows, backward gotos will succeed on non-seekable inputs.)
 
    Expressions
        The if, while and exit builtin commands use expressions with  a  common
        syntax.   The expressions can include any of the operators described in
        the next three sections.  Note that the @ builtin  command  (q.v.)  has
        its own separate syntax.
 
    Logical, arithmetical and comparison operators
        These operators are similar to those of C and have the same precedence.
        They include
 
            ||  &&  |  ^  &  ==  !=  =~  !~  <=  >=
            <  > <<  >>  +  -  *  /  %  !  ~  (  )
 
        Here the precedence increases to the right, ‘==’ ‘!=’  ‘=~’  and  ‘!~’,
        ‘<=’  ‘>=’  ‘<’  and  ‘>’,  ‘<<’ and ‘>>’, ‘+’ and ‘-’, ‘*’ ‘/’ and ‘%’
        being, in groups, at the same level.  The ‘==’ ‘!=’ ‘=~’ and ‘!~’ oper‐
        ators  compare  their  arguments as strings; all others operate on num‐
        bers.  The operators ‘=~’ and ‘!~’ are like ‘!=’ and ‘==’  except  that
        the  right  hand  side  is  a  glob-pattern (see Filename substitution)
        against which the left hand operand is matched.  This reduces the  need
        for use of the switch builtin command in shell scripts when all that is
        really needed is pattern matching.
 
        Strings which begin with ‘0’ are considered  octal  numbers.   Null  or
        missing  arguments  are considered ‘0’.  The results of all expressions
        are strings, which represent decimal numbers.  It is important to  note
        that  no  two  components of an expression can appear in the same word;
        except when adjacent to components of expressions which  are  syntacti‐
        cally  significant  to the parser (‘&’ ‘|’ ‘<’ ‘>’ ‘(’ ‘)’) they should
        be surrounded by spaces.
 
    Command exit status
        Commands can be executed in expressions and their exit status  returned
        by enclosing them in braces (‘{}’).  Remember that the braces should be
        separated from the words of the command by spaces.  Command  executions
        succeed, returning true, i.e., ‘1’, if the command exits with status 0,
        otherwise they fail, returning false, i.e., ‘0’.  If more detailed sta‐
        tus information is required then the command should be executed outside
        of an expression and the status shell variable examined.
 
    File inquiry operators
        Some of these operators perform true/false tests on files  and  related
        objects.  They are of the form -op file, where op is one of
 
            r   Read access
            w   Write access
            x   Execute access
            X   Executable  in the path or shell builtin, e.g., ‘-X ls’ and ‘-X
                ls-F’ are generally true, but ‘-X /bin/ls’ is not (+)
            e   Existence
            o   Ownership
            z   Zero size
            s   Non-zero size (+)
            f   Plain file
            d   Directory
            l   Symbolic link (+) *
            b   Block special file (+)
            c   Character special file (+)
            p   Named pipe (fifo) (+) *
            S   Socket special file (+) *
            u   Set-user-ID bit is set (+)
            g   Set-group-ID bit is set (+)
            k   Sticky bit is set (+)
            t   file (which must be a digit) is an open file descriptor  for  a
                terminal device (+)
            R   Has been migrated (convex only) (+)
            L   Applies  subsequent  operators in a multiple-operator test to a
                symbolic link rather than to the file to which the link  points
                (+) *
 
        file  is command and filename expanded and then tested to see if it has
        the specified relationship to the real user.  If file does not exist or
        is  inaccessible  or, for the operators indicated by ‘*’, if the speci‐
        fied file type does not exist on the current system, then all enquiries
        return false, i.e., ‘0’.
 
        These  operators may be combined for conciseness: ‘-xy file’ is equiva‐
        lent to ‘-x file && -y file’.  (+) For example, ‘-fx’ is true  (returns
        ‘1’) for plain executable files, but not for directories.
 
        L may be used in a multiple-operator test to apply subsequent operators
        to a symbolic link rather than to the file to which  the  link  points.
        For  example, ‘-lLo’ is true for links owned by the invoking user.  Lr,
        Lw and Lx are always true for links and false for non-links.  L  has  a
        different  meaning  when it is the last operator in a multiple-operator
        test; see below.
 
        It is possible but not useful, and  sometimes  misleading,  to  combine
        operators  which  expect file to be a file with operators which do not,
        (e.g., X and t).  Following L with a non-file operator can lead to par‐
        ticularly strange results.
 
        Other  operators  return  other information, i.e., not just ‘0’ or ‘1’.
        (+) They have the same format as before; op may be one of
 
            A       Last file access time, as the number of seconds  since  the
                    epoch
            A:      Like A, but in timestamp format, e.g., ‘Fri May 14 16:36:10
                    1993’
            M       Last file modification time
            M:      Like M, but in timestamp format
            C       Last inode modification time
            C:      Like C, but in timestamp format
            D       Device number
            I       Inode number
            F       Composite file identifier, in the form device:inode
            L       The name of the file pointed to by a symbolic link
            N       Number of (hard) links
            P       Permissions, in octal, without leading zero
            P:      Like P, with leading zero
            Pmode   Equivalent to ‘-P file & mode’, e.g., ‘-P22  file’  returns
                    ‘22’  if  file  is  writable by group and other, ‘20’ if by
                    group only, and ‘0’ if by neither
            Pmode:  Like Pmode:, with leading zero
            U       Numeric userid
            U:      Username, or the numeric userid if the username is unknown
            G       Numeric groupid
            G:      Groupname, or the  numeric  groupid  if  the  groupname  is
                    unknown
            Z       Size, in bytes
 
        Only one of these operators may appear in a multiple-operator test, and
        it must be the last.  Note that L has a different meaning at the end of
        and  elsewhere  in  a  multiple-operator  test.  Because ‘0’ is a valid
        return value for many of these operators, they do not return  ‘0’  when
        they fail: most return ‘-1’, and F returns ‘:’.
 
        If  the  shell  is  compiled  with POSIX defined (see the version shell
        variable), the result of a file inquiry is based on the permission bits
        of  the  file  and not on the result of the access(2) system call.  For
        example, if one tests a file with -w whose permissions would ordinarily
        allow writing but which is on a file system mounted read-only, the test
        will succeed in a POSIX shell but fail in a non-POSIX shell.
 
        File inquiry operators can also be evaluated with the filetest  builtin
        command (q.v.) (+).
 
    Jobs
        The  shell  associates  a  job with each pipeline.  It keeps a table of
        current jobs, printed by the jobs command, and assigns them small inte‐
        ger  numbers.  When a job is started asynchronously with ‘&’, the shell
        prints a line which looks like
 
            [1] 1234
 
        indicating that the job which was started asynchronously was job number
        1 and had one (top-level) process, whose process id was 1234.
 
        If  you are running a job and wish to do something else you may hit the
        suspend key (usually ‘^Z’), which sends a STOP signal  to  the  current
        job.  The shell will then normally indicate that the job has been ‘Sus‐
        pended’ and print another prompt.  If the listjobs  shell  variable  is
        set,  all  jobs  will be listed like the jobs builtin command; if it is
        set to ‘long’ the listing will be in long format, like ‘jobs -l’.   You
        can  then manipulate the state of the suspended job.  You can put it in
        the ‘‘background’’ with the bg command or run some other  commands  and
        eventually  bring  the  job back into the ‘‘foreground’’ with fg.  (See
        also the run-fg-editor editor command.)  A ‘^Z’  takes  effect  immedi‐
        ately  and is like an interrupt in that pending output and unread input
        are discarded when it is typed.  The wait builtin  command  causes  the
        shell to wait for all background jobs to complete.
 
        The  ‘^]’ key sends a delayed suspend signal, which does not generate a
        STOP signal until a program attempts to read(2) it, to the current job.
        This  can  usefully be typed ahead when you have prepared some commands
        for a job which you wish to stop after it has read them.  The ‘^Y’  key
        performs  this function in csh(1); in tcsh, ‘^Y’ is an editing command.
        (+)
 
        A job being run in the background stops if it tries to  read  from  the
        terminal.   Background jobs are normally allowed to produce output, but
        this can be disabled by giving the command ‘stty tostop’.  If  you  set
        this  tty  option, then background jobs will stop when they try to pro‐
        duce output like they do when they try to read input.
 
        There are several ways to refer to jobs in the  shell.   The  character
        ‘%’  introduces  a job name.  If you wish to refer to job number 1, you
        can name it as ‘%1’.  Just naming a job brings it  to  the  foreground;
        thus  ‘%1’ is a synonym for ‘fg %1’, bringing job 1 back into the fore‐
        ground.  Similarly, saying ‘%1 &’ resumes job 1 in the background, just
        like  ‘bg %1’.  A job can also be named by an unambiguous prefix of the
        string typed in to start it: ‘%ex’ would normally restart  a  suspended
        ex(1)  job,  if there were only one suspended job whose name began with
        the string ‘ex’.  It is also possible to say ‘%?string’  to  specify  a
        job whose text contains string, if there is only one such job.
 
        The shell maintains a notion of the current and previous jobs.  In out‐
        put pertaining to jobs, the current job is marked with a  ‘+’  and  the
        previous  job with a ‘-’.  The abbreviations ‘%+’, ‘%’, and (by analogy
        with the syntax of the history mechanism) ‘%%’ all refer to the current
        job, and ‘%-’ refers to the previous job.
 
        The job control mechanism requires that the stty(1) option ‘new’ be set
        on some systems.  It is an artifact from a ‘new’ implementation of  the
        tty  driver  which  allows  generation of interrupt characters from the
        keyboard to tell jobs to stop.  See stty(1) and the setty builtin  com‐
        mand for details on setting options in the new tty driver.
 
    Status reporting
        The shell learns immediately whenever a process changes state.  It nor‐
        mally informs you whenever a job becomes blocked  so  that  no  further
        progress  is  possible, but only right before it prints a prompt.  This
        is done so that it does not otherwise disturb your work.  If,  however,
        you  set  the  shell variable notify, the shell will notify you immedi‐
        ately of changes of status in background jobs.  There is also  a  shell
        command  notify which marks a single process so that its status changes
        will be immediately reported.  By default notify marks the current pro‐
        cess; simply say ‘notify’ after starting a background job to mark it.
 
        When  you  try  to  leave the shell while jobs are stopped, you will be
        warned that ‘You have stopped jobs.’ You may use the  jobs  command  to
        see  what  they  are.  If you do this or immediately try to exit again,
        the shell will not warn you a second time, and the suspended jobs  will
        be terminated.
 
    Automatic, periodic and timed events (+)
        There are various ways to run commands and take other actions automati‐
        cally at various times in the ‘‘life cycle’’ of the  shell.   They  are
        summarized  here, and described in detail under the appropriate Builtin
        commands, Special shell variables and Special aliases.
 
        The sched builtin command puts commands in a scheduled-event  list,  to
        be executed by the shell at a given time.
 
        The  beepcmd,  cwdcmd,  periodic,  precmd,  postcmd, and jobcmd Special
        aliases can be set, respectively, to execute commands  when  the  shell
        wants  to ring the bell, when the working directory changes, every tpe     
        riod minutes, before each prompt, before each  command  gets  executed,
        after  each  command  gets  executed,  and  when a job is started or is
        brought into the foreground.
 
        The autologout shell variable can be set to log out or lock  the  shell
        after a given number of minutes of inactivity.
 
        The  mail shell variable can be set to check for new mail periodically.
 
        The printexitvalue shell variable can be set to print the  exit  status
        of commands which exit with a status other than zero.
 
        The  rmstar  shell  variable can be set to ask the user, when ‘rm *’ is
        typed, if that is really what was meant.
 
        The time shell variable can be set to execute the time builtin  command
        after the completion of any process that takes more than a given number
        of CPU seconds.
 
        The watch and who shell variables can be set to  report  when  selected
        users log in or out, and the log builtin command reports on those users
        at any time.
 
    Native Language System support (+)
        The shell is eight bit clean (if so compiled;  see  the  version  shell
        variable)  and  thus  supports  character sets needing this capability.
        NLS support differs depending on whether or not the shell was  compiled
        to  use  the  system’s NLS (again, see version).  In either case, 7-bit
        ASCII is the default for character classification (e.g., which  charac‐
        ters  are  printable)  and  sorting,  and changing the LANG or LC_CTYPE
        environment variables causes a check  for  possible  changes  in  these
        respects.
 
        When  using  the  system’s  NLS, the setlocale(3) function is called to
        determine appropriate character classification and sorting.  This func‐
        tion  typically  examines  the LANG and LC_CTYPE environment variables;
        refer to the system documentation for further details.  When not  using
        the  system’s  NLS,  the  shell  simulates  it by assuming that the ISO
        8859-1 character set is used whenever either of the LANG  and  LC_CTYPE
        variables are set, regardless of their values.  Sorting is not affected
        for the simulated NLS.
 
        In addition, with both real and simulated NLS, all printable characters
        in  the  range  \200-\377,  i.e.,  those that have M-char bindings, are
        automatically rebound to self-insert-command.  The corresponding  bind‐
        ing for the escape-char sequence, if any, is left alone.  These charac‐
        ters are not rebound if the NOREBIND environment variable is set.  This
        may  be  useful  for  the  simulated  NLS or a primitive real NLS which
        assumes full ISO 8859-1.  Otherwise, all M-char bindings in  the  range
        \240-\377  are  effectively  undone.  Explicitly rebinding the relevant
        keys with bindkey is of course still possible.
 
        Unknown characters (i.e., those that are neither printable nor  control
        characters) are printed in the format \nnn.  If the tty is not in 8 bit
        mode, other 8 bit characters are printed by converting  them  to  ASCII
        and  using  standout mode.  The shell never changes the 7/8 bit mode of
        the tty and tracks user-initiated changes of 7/8 bit mode.   NLS  users
        (or,  for  that  matter,  those who want to use a meta key) may need to
        explicitly set the tty in 8 bit mode through  the  appropriate  stty(1)
        command in, e.g., the ~/.login file.
 
    OS variant support (+)
        A  number  of  new builtin commands are provided to support features in
        particular operating systems.  All  are  described  in  detail  in  the
        Builtin commands section.
 
        On  systems  that  support  TCF  (aix-ibm370,  aix-ps2),  getspath  and
        setspath get and set the system execution path, getxvers  and  setxvers
        get  and  set the experimental version prefix and migrate migrates pro‐
        cesses between sites.  The jobs builtin prints the site on  which  each
        job is executing.
 
        Under  Domain/OS,  inlib  adds shared libraries to the current environ‐
        ment, rootnode changes the rootnode and ver changes the systype.
 
        Under Mach, setpath is equivalent to Mach’s setpath(1).
 
        Under Masscomp/RTU and Harris CX/UX, universe sets the universe.
 
        Under Harris CX/UX, ucb or att runs a command under the specified  uni‐
        verse.
 
        Under Convex/OS, warp prints or sets the universe.
 
        The  VENDOR, OSTYPE and MACHTYPE environment variables indicate respec‐
        tively the vendor, operating system and  machine  type  (microprocessor
        class  or  machine model) of the system on which the shell thinks it is
        running.  These are particularly useful when sharing one’s home  direc‐
        tory between several types of machines; one can, for example,
 
            set path = (~/bin.$MACHTYPE /usr/ucb /bin /usr/bin .)
 
        in  one’s ~/.login and put executables compiled for each machine in the
        appropriate directory.
 
        The version shell variable indicates what options were chosen when  the
        shell was compiled.
 
        Note  also  the  newgrp builtin, the afsuser and echo_style shell vari‐
        ables and the system-dependent locations of  the  shell’s  input  files
        (see FILES).
 
    Signal handling
        Login  shells  ignore  interrupts when reading the file ~/.logout.  The
        shell ignores quit signals unless started with -q.  Login shells  catch
        the terminate signal, but non-login shells inherit the terminate behav‐
        ior from their parents.  Other signals have the values which the  shell
        inherited from its parent.
 
        In  shell scripts, the shell’s handling of interrupt and terminate sig‐
        nals can be controlled with onintr, and its handling of hangups can  be
        controlled with hup and nohup.
 
        The  shell  exits on a hangup (see also the logout shell variable).  By
        default, the shell’s children do too, but the shell does not send  them
        a hangup when it exits.  hup arranges for the shell to send a hangup to
        a child when it exits, and nohup sets a child to ignore hangups.
 
    Terminal management (+)
        The shell uses  three  different  sets  of  terminal  (‘‘tty’’)  modes:
        ‘edit’,  used  when editing, ‘quote’, used when quoting literal charac‐
        ters, and ‘execute’, used when executing  commands.   The  shell  holds
        some settings in each mode constant, so commands which leave the tty in
        a confused state do not interfere  with  the  shell.   The  shell  also
        matches  changes  in the speed and padding of the tty.  The list of tty
        modes that are kept constant can be  examined  and  modified  with  the
        setty  builtin.  Note that although the editor uses CBREAK mode (or its
        equivalent), it takes typed-ahead characters anyway.
 
        The echotc, settc and telltc commands can be  used  to  manipulate  and
        debug terminal capabilities from the command line.
 
        On  systems  that  support  SIGWINCH  or SIGWINDOW, the shell adapts to
        window resizing automatically and  adjusts  the  environment  variables
        LINES and COLUMNS if set.  If the environment variable TERMCAP contains
        li# and co# fields, the shell adjusts them to reflect  the  new  window
        size.
 

REFERENCE

        The  next sections of this manual describe all of the available Builtin
        commands, Special aliases and Special shell variables.
 
    Builtin commands
        %job    A synonym for the fg builtin command.
 
        %job &  A synonym for the bg builtin command.
 
        :       Does nothing, successfully.
 
        @
        @ name = expr
        @ name[index] = expr
        @ name++|--
        @ name[index]++|--
                The first form prints the values of all shell variables.
 
                The second form assigns the value of expr to name.   The  third
                form  assigns  the  value  of expr to the index’th component of
                name; both name and its index’th component must already  exist.
 
                expr  may  contain  the  operators ‘*’, ‘+’, etc., as in C.  If
                expr contains ‘<’, ‘>’, ‘&’ or ‘’ then at least  that  part  of
                expr  must be placed within ‘()’.  Note that the syntax of expr
                has nothing to do with that described under Expressions.
 
                The fourth and fifth forms increment (‘++’) or decrement (‘--’)
                name or its index’th component.
 
                The space between ‘@’ and name is required.  The spaces between
                name and ‘=’ and between ‘=’ and expr are optional.  Components
                of expr must be separated by spaces.
 
        alias [name [wordlist]]
                Without  arguments,  prints all aliases.  With name, prints the
                alias for name.  With name and wordlist,  assigns  wordlist  as
                the  alias  of  name.  wordlist is command and filename substi‐
                tuted.  name may not be ‘alias’ or  ‘unalias’.   See  also  the
                unalias builtin command.
 
        alloc   Shows  the  amount of dynamic memory acquired, broken down into
                used and free memory.  With an argument  shows  the  number  of
                free  and  used  blocks  in each size category.  The categories
                start at size 8 and double at each step.  This command’s output
                may  vary  across  system types, because systems other than the
                VAX may use a different memory allocator.
 
        bg [%job ...]
                Puts the specified jobs (or,  without  arguments,  the  current
                job)  into  the  background,  continuing each if it is stopped.
                job may be a number, a string, ‘’, ‘%’, ‘+’ or ‘-’ as described
                under Jobs.
 
        bindkey [-l|-d|-e|-v|-u] (+)
        bindkey [-a] [-b] [-k] [-r] [--] key (+)
        bindkey [-a] [-b] [-k] [-c|-s] [--] key command (+)
                Without  options,  the  first form lists all bound keys and the
                editor command to which each is bound, the  second  form  lists
                the  editor  command  to  which key is bound and the third form
                binds the editor command command to key.  Options include:
 
                -l  Lists all editor commands and a short description of  each.
                -d  Binds  all  keys  to  the standard bindings for the default
                    editor.
                -e  Binds all keys to the standard GNU Emacs-like bindings.
                -v  Binds all keys to the standard vi(1)-like bindings.
                -a  Lists or changes key-bindings in the alternative  key  map.
                    This is the key map used in vi command mode.
                -b  key  is interpreted as a control character written ^charac‐
                    ter (e.g., ‘^A’) or C-character (e.g., ‘C-A’), a meta char‐
                    acter  written  M-character  (e.g.,  ‘M-A’), a function key
                    written F-string (e.g., ‘F-string’), or an extended  prefix
                    key written X-character (e.g., ‘X-A’).
                -k  key  is interpreted as a symbolic arrow key name, which may
                    be one of ‘down’, ‘up’, ‘left’ or ‘right’.
                -r  Removes key’s binding.  Be careful: ‘bindkey -r’  does  not
                    bind key to self-insert-command (q.v.), it unbinds key com‐
                    pletely.
                -c  command is interpreted as a  builtin  or  external  command
                    instead of an editor command.
                -s  command  is taken as a literal string and treated as termi‐
                    nal input when key is typed.  Bound  keys  in  command  are
                    themselves reinterpreted, and this continues for ten levels
                    of interpretation.
                --  Forces a break from option processing, so the next word  is
                    taken as key even if it begins with ’-’.
                -u (or any invalid option)
                    Prints a usage message.
 
                key  may  be  a  single character or a string.  If a command is
                bound to a string, the first character of the string  is  bound
                to  sequence-lead-in and the entire string is bound to the com‐
                mand.
 
                Control characters in key can be literal (they can be typed  by
                preceding  them with the editor command quoted-insert, normally
                bound to ‘^V’) or written caret-character  style,  e.g.,  ‘^A’.
                Delete is written ‘^?’  (caret-question mark).  key and command
                can contain backslashed escape sequences (in the style of  Sys‐
                tem V echo(1)) as follows:
 
                    \a      Bell
                    \b      Backspace
                    \e      Escape
                    \f      Form feed
                    \n      Newline
                    \r      Carriage return
                    \t      Horizontal tab
                    \v      Vertical tab
                    \nnn    The ASCII character corresponding to the octal num‐
                            ber nnn
 
                ‘\’ nullifies the special meaning of the  following  character,
                if it has any, notably ‘\’ and ‘^’.
 
        break   Causes execution to resume after the end of the nearest enclos‐
                ing foreach or while.  The remaining commands  on  the  current
                line  are  executed.   Multi-level  breaks are thus possible by
                writing them all on one line.
 
        breaksw Causes a break from a switch, resuming after the endsw.
 
        builtins (+)
                Prints the names of all builtin commands.
 
        bye (+) A synonym for the logout builtin command.   Available  only  if
                the shell was so compiled; see the version shell variable.
 
        case label:
                A label in a switch statement as discussed below.
 
        cd [-p] [-l] [-n|-v] [name]
                If  a  directory  name  is  given,  changes the shell’s working
                directory to name.  If not, changes to home.  If name is ‘-’ it
                is  interpreted  as  the  previous working directory (see Other
                substitutions).  (+) If name is not a subdirectory of the  cur‐
                rent  directory  (and  does not begin with ‘/’, ‘./’ or ‘../’),
                each component of the variable cdpath is checked to see  if  it
                has  a  subdirectory name.  Finally, if all else fails but name
                is a shell variable whose value begins with ‘/’, then  this  is
                tried to see if it is a directory.
 
                With -p, prints the final directory stack, just like dirs.  The
                -l, -n and -v flags have the same effect on cd as on dirs,  and
                they imply -p.  (+)
 
                See also the implicitcd shell variable.
 
        chdir   A synonym for the cd builtin command.
 
        complete [command [word/pattern/list[:select]/[[suffix]/] ...]] (+)
                Without  arguments, lists all completions.  With command, lists
                completions for command.  With command and word  etc.,  defines
                completions.
 
                command may be a full command name or a glob-pattern (see File     
                name substitution).  It can begin with  ‘-’  to  indicate  that
                completion should be used only when command is ambiguous.
 
                word specifies which word relative to the current word is to be
                completed, and may be one of the following:
 
                    c   Current-word completion.   pattern  is  a  glob-pattern
                        which  must  match the beginning of the current word on
                        the command line.  pattern is ignored  when  completing
                        the current word.
                    C   Like  c,  but includes pattern when completing the cur‐
                        rent word.
                    n   Next-word completion.  pattern is a glob-pattern  which
                        must  match  the  beginning of the previous word on the
                        command line.
                    N   Like n, but must match the beginning of  the  word  two
                        before the current word.
                    p   Position-dependent  completion.   pattern  is a numeric
                        range, with the same syntax used to index  shell  vari‐
                        ables, which must include the current word.
 
                list,  the list of possible completions, may be one of the fol‐
                lowing:
 
                    a       Aliases
                    b       Bindings (editor commands)
                    c       Commands (builtin or external commands)
                    C       External commands which  begin  with  the  supplied
                            path prefix
                    d       Directories
                    D       Directories which begin with the supplied path pre‐
                            fix
                    e       Environment variables
                    f       Filenames
                    F       Filenames which begin with the supplied path prefix
                    g       Groupnames
                    j       Jobs
                    l       Limits
                    n       Nothing
                    s       Shell variables
                    S       Signals
                    t       Plain (‘‘text’’) files
                    T       Plain  (‘‘text’’)  files  which begin with the sup‐
                            plied path prefix
                    v       Any variables
                    u       Usernames
                    x       Like n, but  prints  select  when  list-choices  is
                            used.
                    X       Completions
                    $var    Words from the variable var
                    (...)   Words from the given list
                    ‘...‘   Words from the output of command
 
                select  is an optional glob-pattern.  If given, words from only
                list that match select are considered  and  the  fignore  shell
                variable  is  ignored.   The last three types of completion may
                not have a select pattern, and x uses select as an  explanatory
                message when the list-choices editor command is used.
 
                suffix  is  a  single  character to be appended to a successful
                completion.  If null, no character is appended.  If omitted (in
                which  case  the fourth delimiter can also be omitted), a slash
                is appended to directories and a space to other words.
 
                Now for some examples.  Some commands take only directories  as
                arguments, so there’s no point completing plain files.
 
                    > complete cd ’p/1/d/’
 
                completes  only  the  first  word following ‘cd’ (‘p/1’) with a
                directory.  p-type completion can also be used to  narrow  down
                command completion:
 
                    > co[^D]
                    complete compress
                    > complete -co* ’p/0/(compress)/’
                    > co[^D]
                    > compress
 
                This completion completes commands (words in position 0, ‘p/0’)
                which begin with ‘co’ (thus matching ‘co*’) to ‘compress’  (the
                only  word  in  the list).  The leading ‘-’ indicates that this
                completion is to be used with only ambiguous commands.
 
                    > complete find ’n/-user/u/’
 
                is an example of n-type completion.  Any word following  ‘find’
                and immediately following ‘-user’ is completed from the list of
                users.
 
                    > complete cc ’c/-I/d/’
 
                demonstrates c-type completion.  Any word  following  ‘cc’  and
                beginning  with  ‘-I’ is completed as a directory.  ‘-I’ is not
                taken as part of the directory because we used lowercase c.
 
                Different lists are useful with different commands.
 
                    > complete alias ’p/1/a/’
                    > complete man ’p/*/c/’
                    > complete set ’p/1/s/’
                    > complete true ’p/1/x:Truth has no options./’
 
                These complete words following ‘alias’ with aliases, ‘man’ with
                commands,  and ‘set’ with shell variables.  ‘true’ doesn’t have
                any options, so x does nothing when completion is attempted and
                prints  ‘Truth  has  no  options.’  when completion choices are
                listed.
 
                Note that the man example, and several  other  examples  below,
                could just as well have used ’c/*’ or ’n/*’ as ’p/*’.
 
                Words  can be completed from a variable evaluated at completion
                time,
 
                    > complete ftp ’p/1/$hostnames/’
                    > set hostnames = (rtfm.mit.edu tesla.ee.cornell.edu)
                    > ftp [^D]
                    rtfm.mit.edu tesla.ee.cornell.edu
                    > ftp [^C]
                    >  set  hostnames  =   (rtfm.mit.edu   tesla.ee.cornell.edu
                    uunet.uu.net)
                    > ftp [^D]
                    rtfm.mit.edu tesla.ee.cornell.edu uunet.uu.net
 
                or from a command run at completion time:
 
                    > complete kill ’p/*/‘ps | awk \{print\ \$1\}‘/’
                    > kill -9 [^D]
                    23113 23377 23380 23406 23429 23529 23530 PID
 
                Note  that the complete command does not itself quote its argu‐
                ments, so the braces, space and ‘$’ in  ‘{print  $1}’  must  be
                quoted explicitly.
 
                One command can have multiple completions:
 
                    > complete dbx ’p/2/(core)/’ ’p/*/c/’
 
                completes the second argument to ‘dbx’ with the word ‘core’ and
                all other arguments with commands.  Note  that  the  positional
                completion   is  specified  before  the  next-word  completion.
                Because completions are evaluated from left to  right,  if  the
                next-word completion were specified first it would always match
                and the positional completion would never be executed.  This is
                a common mistake when defining a completion.
 
                The  select  pattern  is useful when a command takes files with
                only particular forms as arguments.  For example,
 
                    > complete cc ’p/*/f:*.[cao]/’
 
                completes ‘cc’ arguments to files ending in only ‘.c’, ‘.a’, or
                ‘.o’.  select can also exclude files, using negation of a glob-
                pattern as described under Filename  substitution.   One  might
                use
 
                    > complete rm ’p/*/f:^*.{c,h,cc,C,tex,1,man,l,y}/’
 
                to  exclude  precious  source  code  from  ‘rm’ completion.  Of
                course, one could still type excluded names manually  or  over‐
                ride  the  completion  mechanism using the complete-word-raw or
                list-choices-raw editor commands (q.v.).
 
                The ‘C’, ‘D’, ‘F’ and ‘T’ lists are like ‘c’, ‘d’, ‘f’ and  ‘t’
                respectively,  but  they use the select argument in a different
                way: to restrict completion to files beginning with a  particu‐
                lar path prefix.  For example, the Elm mail program uses ‘=’ as
                an abbreviation for one’s mail directory.  One might use
 
                    > complete elm c@=@F:$HOME/Mail/@
 
                to complete ‘elm -f =’ as if it were ‘elm  -f  ~/Mail/’.   Note
                that  we  used  ‘@’  instead of ‘/’ to avoid confusion with the
                select argument, and we used ‘$HOME’  instead  of  ‘~’  because
                home  directory  substitution  works at only the beginning of a
                word.
 
                suffix is used to add a nonstandard suffix (not  space  or  ‘/’
                for directories) to completed words.
 
                    > complete finger ’c/*@/$hostnames/’ ’p/1/u/@’
 
                completes arguments to ‘finger’ from the list of users, appends
                an ‘@’, and then completes after the ‘@’ from  the  ‘hostnames’
                variable.   Note  again  the order in which the completions are
                specified.
 
                Finally, here’s a complex example for inspiration:
 
                    > complete find \
                    ´n/-name/f/’ ’n/-newer/f/’ ’n/-{,n}cpio/f/’ \
                    ´n/-exec/c/’ ’n/-ok/c/’ ’n/-user/u/’ \
                    ´n/-group/g/’ ’n/-fstype/(nfs 4.2)/’ \
                    ´n/-type/(b c d f l p s)/’ \
                    ´c/-/(name newer cpio ncpio exec ok user \
                    group fstype type atime ctime depth inum \
                    ls mtime nogroup nouser perm print prune \
                    size xdev)/’ \
                    ´p/*/d/’
 
                This completes words following ‘-name’,  ‘-newer’,  ‘-cpio’  or
                ‘ncpio’  (note  the pattern which matches both) to files, words
                following ‘-exec’ or ‘-ok’ to commands, words following  ‘user’
                and  ‘group’ to users and groups respectively and words follow‐
                ing ‘-fstype’ or ‘-type’ to members of  the  given  lists.   It
                also  completes  the  switches  themselves  from the given list
                (note the use of c-type completion) and completes anything  not
                otherwise completed to a directory.  Whew.
 
                Remember  that  programmed  completions are ignored if the word
                being completed is a tilde substitution (beginning with ‘~’) or
                a  variable  (beginning with ‘$’).  complete is an experimental
                feature, and the syntax may change in future  versions  of  the
                shell.  See also the uncomplete builtin command.
 
        continue
                Continues  execution of the nearest enclosing while or foreach.
                The rest of the commands on the current line are executed.
 
        default:
                Labels the default case in a switch statement.  It should  come
                after all case labels.
 
        dirs [-l] [-n|-v]
        dirs -S|-L [filename] (+)
        dirs -c (+)
                The  first  form  prints  the  directory stack.  The top of the
                stack is at the left and the first directory in  the  stack  is
                the  current  directory.  With -l, ‘~’ or ‘~name’ in the output
                is expanded explicitly to home or  the  pathname  of  the  home
                directory  for  user  name.   (+)  With -n, entries are wrapped
                before they reach the edge of the screen.  (+) With -v, entries
                are  printed  one  per line, preceded by their stack positions.
                (+) If more than one of -n or -v is given, -v takes precedence.
                -p is accepted but does nothing.
 
                With  -S, the second form saves the directory stack to filename
                as a series of cd and  pushd  commands.   With  -L,  the  shell
                sources  filename,  which  is presumably a directory stack file
                saved by the -S option or the savedirs  mechanism.   In  either
                case,  dirsfile is used if filename is not given and ~/.cshdirs
                is used if dirsfile is unset.
 
                Note that login shells  do  the  equivalent  of  ‘dirs  -L’  on
                startup  and,  if  savedirs  is  set, ‘dirs -S’ before exiting.
                Because only ~/.tcshrc is normally sourced  before  ~/.cshdirs,
                dirsfile should be set in ~/.tcshrc rather than ~/.login.
 
                The last form clears the directory stack.
 
        echo [-n] word ...
                Writes  each  word to the shell’s standard output, separated by
                spaces and terminated with a  newline.   The  echo_style  shell
                variable  may  be  set to emulate (or not) the flags and escape
                sequences of the BSD and/or System  V  versions  of  echo;  see
                echo(1).
 
        echotc [-sv] arg ... (+)
                Exercises  the  terminal capabilities (see termcap(5)) in args.
                For example, ’echotc home’ sends the cursor to the  home  posi‐
                tion,  ’echotc  cm  3  10’ sends it to column 3 and row 10, and
                ’echotc ts 0; echo "This is a test."; echotc fs’  prints  "This
                is a test."  in the status line.
 
                If arg is ’baud’, ’cols’, ’lines’, ’meta’ or ’tabs’, prints the
                value of that capability ("yes" or  "no"  indicating  that  the
                terminal does or does not have that capability).  One might use
                this to make the output from a shell  script  less  verbose  on
                slow  terminals, or limit command output to the number of lines
                on the screen:
 
                    > set history=‘echotc lines‘
 
                    > @ history--
                Termcap strings may contain wildcards which will not echo  cor‐
                rectly.   One  should  use  double  quotes when setting a shell
                variable to a terminal capability string, as in  the  following
                example that places the date in the status line:
 
                    > set tosl="‘echotc ts 0‘"
                    > set frsl="‘echotc fs‘"
                    > echo -n "$tosl";date; echo -n "$frsl"
 
                With  -s,  nonexistent  capabilities  return  the  empty string
                rather than causing an error.  With -v, messages are verbose.
 
        else
        end
        endif
        endsw   See the description of  the  foreach,  if,  switch,  and  while
                statements below.
 
        eval arg ...
                Treats  the  arguments  as  input to the shell and executes the
                resulting command(s) in the context of the current shell.  This
                is  usually used to execute commands generated as the result of
                command or variable substitution, because parsing occurs before
                these substitutions.  See tset(1) for a sample use of eval.
 
        exec command
                Executes the specified command in place of the current shell.
 
        exit [expr]
                The shell exits either with the value of the specified expr (an
                expression, as described under Expressions) or,  without  expr,
                with the value of the status variable.
 
        fg [%job ...]
                Brings  the  specified jobs (or, without arguments, the current
                job) into the foreground, continuing each  if  it  is  stopped.
                job may be a number, a string, ‘’, ‘%’, ‘+’ or ‘-’ as described
                under Jobs.  See also the run-fg-editor editor command.
 
        filetest -op file ... (+)
                Applies op (which is a file inquiry operator as described under
                File inquiry operators) to each file and returns the results as
                a space-separated list.
 
        foreach name (wordlist)
        ...
        end     Successively sets the variable name to each member of  wordlist
                and  executes the sequence of commands between this command and
                the matching end.  (Both foreach and end must appear  alone  on
                separate  lines.)   The builtin command continue may be used to
                continue the loop prematurely and the builtin command break  to
                terminate  it  prematurely.  When this command is read from the
                terminal, the loop is read once prompting with ‘foreach? ’  (or
                prompt2)  before  any  statements in the loop are executed.  If
                you make a mistake typing in a loop at the terminal you can rub
                it out.
 
        getspath (+)
                Prints the system execution path.  (TCF only)
 
        getxvers (+)
                Prints the experimental version prefix.  (TCF only)
 
        glob wordlist
                Like  echo,  but  no  ‘\’  escapes are recognized and words are
                delimited by null characters in the output.   Useful  for  pro‐
                grams  which wish to use the shell to filename expand a list of
                words.
 
        goto word
                word is filename and command-substituted to yield a  string  of
                the  form ‘label’.  The shell rewinds its input as much as pos‐
                sible, searches for a line of the form ‘label:’, possibly  pre‐
                ceded  by  blanks  or  tabs, and continues execution after that
                line.
 
        hashstat
                Prints a statistics line indicating how effective the  internal
                hash table has been at locating commands (and avoiding exec’s).
                An exec is attempted for each component of the path  where  the
                hash  function  indicates a possible hit, and in each component
                which does not begin with a ‘/’.
 
                On machines without vfork(2), prints only the number  and  size
                of hash buckets.
 
        history [-hTr] [n]
        history -S|-L|-M [filename] (+)
        history -c (+)
                The  first  form  prints the history event list.  If n is given
                only the n most recent events are printed or saved.   With  -h,
                the  history list is printed without leading numbers.  If -T is
                specified, timestamps are printed also in comment form.   (This
                can be used to produce files suitable for loading with ’history
                -L’ or ’source -h’.)  With -r, the order of  printing  is  most
                recent first rather than oldest first.
 
                With  -S,  the  second form saves the history list to filename.
                If the first word of the savehist shell variable is  set  to  a
                number,  at most that many lines are saved.  If the second word
                of savehist is set to ‘merge’, the history list is merged  with
                the  existing history file instead of replacing it (if there is
                one) and sorted by time stamp.  (+) Merging is intended for  an
                environment  like  the  X  Window System with several shells in
                simultaneous use.  Currently it succeeds only when  the  shells
                quit nicely one after another.
 
                With -L, the shell appends filename, which is presumably a his‐
                tory list saved by the -S option or the savehist mechanism,  to
                the  history list.  -M is like -L, but the contents of filename
                are merged into the history list and sorted by  timestamp.   In
                either  case,  histfile  is  used  if filename is not given and
                ~/.history is used if  histfile  is  unset.   ‘history  -L’  is
                exactly  like  ’source  -h’  except  that it does not require a
                filename.
 
                Note that login shells do the equivalent  of  ‘history  -L’  on
                startup  and,  if savehist is set, ‘history -S’ before exiting.
                Because only ~/.tcshrc is normally sourced  before  ~/.history,
                histfile should be set in ~/.tcshrc rather than ~/.login.
 
                If  histlit  is  set, the first and second forms print and save
                the literal (unexpanded) form of the history list.
 
                The last form clears the history list.
 
        hup [command] (+)
                With command, runs command such that it will exit on  a  hangup
                signal  and  arranges  for the shell to send it a hangup signal
                when the shell exits.  Note that commands  may  set  their  own
                response  to  hangups,  overriding  hup.   Without  an argument
                (allowed in only a shell script), causes the shell to exit on a
                hangup  for  the remainder of the script.  See also Signal han     
                dling and the nohup builtin command.
 
        if (expr) command
                If expr (an expression, as described under Expressions)  evalu‐
                ates  true, then command is executed.  Variable substitution on
                command happens early, at the same time it does for the rest of
                the  if  command.   command  must  be  a simple command, not an
                alias, a pipeline, a command list or  a  parenthesized  command
                list,  but  it  may  have  arguments.  Input/output redirection
                occurs even if expr is false and command is thus not  executed;
                this is a bug.
 
        if (expr) then
        ...
        else if (expr2) then
        ...
        else
        ...
        endif   If  the  specified  expr is true then the commands to the first
                else are executed; otherwise if expr2 is true then the commands
                to  the  second  else are executed, etc.  Any number of else-if
                pairs are possible; only one endif is needed.  The else part is
                likewise  optional.   (The  words else and endif must appear at
                the beginning of input lines; the if must appear alone  on  its
                input line or after an else.)
 
        inlib shared-library ... (+)
                Adds  each shared-library to the current environment.  There is
                no way to remove a shared library.  (Domain/OS only)
 
        jobs [-l]
                Lists the active jobs.  With -l, lists process IDs in  addition
                to  the normal information.  On TCF systems, prints the site on
                which each job is executing.
 
        kill [-s signal] %job|pid ...
        kill -l The first and second forms sends the specified signal  (or,  if
                none  is  given,  the TERM (terminate) signal) to the specified
                jobs or processes.  job may be a number, a string, ‘’, ‘%’, ‘+’
                or  ‘-’  as  described under Jobs.  Signals are either given by
                number or by name (as given in /usr/include/signal.h,  stripped
                of  the  prefix  ‘SIG’).   There is no default job; saying just
                ‘kill’ does not send a signal to the current job.  If the  sig‐
                nal  being  sent  is TERM (terminate) or HUP (hangup), then the
                job or process is sent a CONT (continue) signal as  well.   The
                third form lists the signal names.
 
        limit [-h] [resource [maximum-use]]
                Limits  the consumption by the current process and each process
                it creates to not individually exceed maximum-use on the speci‐
                fied  resource.   If  no maximum-use is given, then the current
                limit is printed; if no resource is given, then all limitations
                are  given.   If the -h flag is given, the hard limits are used
                instead of the current limits.  The hard limits impose a  ceil‐
                ing  on  the values of the current limits.  Only the super-user
                may raise the hard limits, but a user may lower  or  raise  the
                current limits within the legal range.
 
                Controllable  resources  currently include (if supported by the
                OS):
 
                cputime
                       the maximum number of cpu-seconds to  be  used  by  each
                       process
 
                filesize
                       the largest single file which can be created
 
                datasize
                       the  maximum growth of the data+stack region via sbrk(2)
                       beyond the end of the program text
 
                stacksize
                       the maximum size  of  the  automatically-extended  stack
                       region
 
                coredumpsize
                       the size of the largest core dump that will be created
 
                memoryuse
                       the maximum amount of physical memory a process may have
                       allocated to it at a given time
 
                descriptors or openfiles
                       the maximum number of open files for this process
 
                concurrency
                       the maximum number of threads for this process
 
                memorylocked
                       the maximum size which a process may  lock  into  memory
                       using mlock(2)
 
                maxproc
                       the  maximum  number  of simultaneous processes for this
                       user id
 
                sbsize the maximum size of socket buffer usage for this user
 
                maximum-use may be given as a (floating point or integer)  num‐
                ber  followed  by  a  scale  factor.  For all limits other than
                cputime the default scale is ‘k’ or ‘kilobytes’ (1024 bytes); a
                scale  factor  of  ‘m’  or  ‘megabytes’  may also be used.  For
                cputime the default scaling is ‘seconds’, while ‘m’ for minutes
                or  ‘h’ for hours, or a time of the form ‘mm:ss’ giving minutes
                and seconds may be used.
 
                For both resource names and scale factors, unambiguous prefixes
                of the names suffice.
 
        log (+) Prints  the watch shell variable and reports on each user indi‐
                cated in watch who is logged in, regardless of when  they  last
                logged in.  See also watchlog.
 
        login   Terminates  a  login  shell,  replacing  it with an instance of
                /bin/login. This is one way to log off, included  for  compati‐
                bility with sh(1).
 
        logout  Terminates  a  login  shell.  Especially useful if ignoreeof is
                set.
 
        ls-F [-switch ...] [file ...] (+)
                Lists files like ‘ls -F’, but much faster.  It identifies  each
                type of special file in the listing with a special character:
 
                /   Directory
                *   Executable
                #   Block device
                %   Character device
                |   Named pipe (systems with named pipes only)
                =   Socket (systems with sockets only)
                @   Symbolic link (systems with symbolic links only)
                +   Hidden  directory  (AIX  only)  or context dependent (HP/UX
                    only)
                :   Network special (HP/UX only)
 
                If the listlinks shell variable  is  set,  symbolic  links  are
                identified  in  more detail (on only systems that have them, of
                course):
 
                @   Symbolic link to a non-directory
                >   Symbolic link to a directory
                &   Symbolic link to nowhere
 
                listlinks also slows down ls-F and  causes  partitions  holding
                files pointed to by symbolic links to be mounted.
 
                If  the  listflags shell variable is set to ‘x’, ‘a’ or ‘A’, or
                any combination thereof (e.g., ‘xA’), they are used as flags to
                ls-F, making it act like ‘ls -xF’, ‘ls -Fa’, ‘ls -FA’ or a com‐
                bination (e.g., ‘ls -FxA’).  On machines where ‘ls -C’  is  not
                the default, ls-F acts like ‘ls -CF’, unless listflags contains
                an ‘x’, in which case it acts like ‘ls -xF’.  ls-F  passes  its
                arguments  to  ls(1)  if it is given any switches, so ‘alias ls
                ls-F’ generally does the right thing.
 
                The ls-F builtin can list files using different colors  depend‐
                ing  on the filetype or extension.  See the color tcsh variable
                and the LS_COLORS environment variable.
 
        migrate [-site] pid|%jobid ... (+)
        migrate -site (+)
                The first form migrates the process or job to the  site  speci‐
                fied  or  the  default site determined by the system path.  The
                second form is equivalent to ‘migrate -site  $$’:  it  migrates
                the current process to the specified site.  Migrating the shell
                itself can cause unexpected behavior, because  the  shell  does
                not like to lose its tty.  (TCF only)
 
        newgrp [-] group (+)
                Equivalent  to ‘exec newgrp’; see newgrp(1).  Available only if
                the shell was so compiled; see the version shell variable.
 
        nice [+number] [command]
                Sets the scheduling priority for the shell to number, or, with‐
                out  number, to 4.  With command, runs command at the appropri‐
                ate priority.  The greater the number, the less cpu the process
                gets.   The  super-user  may specify negative priority by using
                ‘nice -number ...’.  Command is always executed in a sub-shell,
                and the restrictions placed on commands in simple if statements
                apply.
 
        nohup [command]
                With command, runs command such that it will ignore hangup sig‐
                nals.   Note  that  commands  may  set  their  own  response to
                hangups, overriding nohup.  Without  an  argument  (allowed  in
                only  a  shell  script), causes the shell to ignore hangups for
                the remainder of the script.  See also Signal handling and  the
                hup builtin command.
 
        notify [%job ...]
                Causes  the  shell  to  notify the user asynchronously when the
                status of any of the specified jobs (or, without %job, the cur‐
                rent  job) changes, instead of waiting until the next prompt as
                is usual.  job may be a number, a string, ‘’, ‘%’, ‘+’  or  ‘-’
                as described under Jobs.  See also the notify shell variable.
 
        onintr [-|label]
                Controls  the action of the shell on interrupts.  Without argu‐
                ments, restores the default action of the shell on  interrupts,
                which  is to terminate shell scripts or to return to the termi‐
                nal command input level.  With ‘-’, causes all interrupts to be
                ignored.   With  label,  causes  the  shell  to execute a ‘goto
                label’ when an interrupt is received or a child process  termi‐
                nates because it was interrupted.
 
                onintr  is ignored if the shell is running detached and in sys‐
                tem startup files (see FILES), where  interrupts  are  disabled
                anyway.
 
        popd [-p] [-l] [-n|-v] [+n]
                Without  arguments, pops the directory stack and returns to the
                new top directory.  With a number ‘+n’, discards the n’th entry
                in the stack.
 
                Finally,  all  forms  of  popd print the final directory stack,
                just like dirs.  The pushdsilent shell variable can be  set  to
                prevent  this and the -p flag can be given to override pushdsi     
                lent.  The -l, -n and -v flags have the same effect on popd  as
                on dirs.  (+)
 
        printenv [name] (+)
                Prints  the  names  and values of all environment variables or,
                with name, the value of the environment variable name.
 
        pushd [-p] [-l] [-n|-v] [name|+n]
                Without arguments, exchanges the top two elements of the direc‐
                tory  stack.   If  pushdtohome  is set, pushd without arguments
                does ‘pushd ~’, like cd.  (+) With  name,  pushes  the  current
                working directory onto the directory stack and changes to name.
                If name is ‘-’ it is interpreted as the previous working direc‐
                tory (see Filename substitution).  (+) If dunique is set, pushd
                removes any instances of name from the stack before pushing  it
                onto  the  stack.  (+) With a number ‘+n’, rotates the nth ele‐
                ment of the directory stack around to be the  top  element  and
                changes  to  it.   If  dextract  is  set,  however,  ‘pushd +n’
                extracts the nth directory, pushes it onto the top of the stack
                and changes to it.  (+)
 
                Finally,  all  forms  of pushd print the final directory stack,
                just like dirs.  The pushdsilent shell variable can be  set  to
                prevent  this and the -p flag can be given to override pushdsi     
                lent.  The -l, -n and -v flags have the same effect on pushd as
                on dirs.  (+)
 
        rehash  Causes  the internal hash table of the contents of the directo‐
                ries in the path variable to be recomputed.  This is needed  if
                new  commands  are  added  to directories in path while you are
                logged in.  This should be necessary only if you  add  commands
                to  one  of  your  own  directories, or if a systems programmer
                changes the contents of one of the  system  directories.   Also
                flushes the cache of home directories built by tilde expansion.
 
        repeat count command
                The specified command, which is subject to  the  same  restric‐
                tions  as  the  command  in the one line if statement above, is
                executed count times.  I/O  redirections  occur  exactly  once,
                even if count is 0.
 
        rootnode //nodename (+)
                Changes  the rootnode to //nodename, so that ‘/’ will be inter‐
                preted as ‘//nodename’.  (Domain/OS only)
 
        sched (+)
        sched [+]hh:mm command (+)
        sched -n (+)
                The first form prints  the  scheduled-event  list.   The  sched
                shell  variable  may  be  set to define the format in which the
                scheduled-event list is printed.  The second form adds  command
                to the scheduled-event list.  For example,
 
                    > sched 11:00 echo It\’s eleven o\’clock.
 
                causes  the shell to echo ‘It’s eleven o’clock.’ at 11 AM.  The
                time may be in 12-hour AM/PM format
 
                    > sched 5pm set prompt=’[%h] It\’s after 5; go home: >’
 
                or may be relative to the current time:
 
                    > sched +2:15 /usr/lib/uucp/uucico -r1 -sother
 
                A relative time specification may not use  AM/PM  format.   The
                third form removes item n from the event list:
 
                    > sched
                         1  Wed Apr  4 15:42  /usr/lib/uucp/uucico -r1 -sother
                         2   Wed Apr  4 17:00  set prompt=[%h] It’s after 5; go
                    home: >
                    > sched -2
                    > sched
                         1  Wed Apr  4 15:42  /usr/lib/uucp/uucico -r1 -sother
 
                A command in the scheduled-event list is executed  just  before
                the  first prompt is printed after the time when the command is
                scheduled.  It is possible to miss the exact time when the com‐
                mand  is  to be run, but an overdue command will execute at the
                next prompt.  A command which comes  due  while  the  shell  is
                waiting  for user input is executed immediately.  However, nor‐
                mal operation of an already-running command will not be  inter‐
                rupted so that a scheduled-event list element may be run.
 
                This  mechanism  is  similar to, but not the same as, the at(1)
                command on some Unix systems.  Its major disadvantage  is  that
                it  may  not  run a command at exactly the specified time.  Its
                major advantage is that because sched runs  directly  from  the
                shell,  it  has access to shell variables and other structures.
                This provides a mechanism for changing one’s  working  environ‐
                ment based on the time of day.
 
        set
        set name ...
        set name=word ...
        set [-r] [-f|-l] name=(wordlist) ... (+)
        set name[index]=word ...
        set -r (+)
        set -r name ... (+)
        set -r name=word ... (+)
                The  first  form  of  the command prints the value of all shell
                variables.  Variables which contain more  than  a  single  word
                print  as a parenthesized word list.  The second form sets name
                to the null string.  The third form sets  name  to  the  single
                word.   The  fourth  form  sets  name  to  the list of words in
                wordlist.  In all cases  the  value  is  command  and  filename
                expanded.   If -r is specified, the value is set read-only.  If
                -f or -l are specified, set only  unique  words  keeping  their
                order.   -f  prefers the first occurrence of a word, and -l the
                last.  The fifth form sets the index’th component  of  name  to
                word;  this component must already exist.  The sixth form lists
                only the names of all shell variables that are read-only.   The
                seventh  form  makes  name  read-only,  whether or not it has a
                value.  The second form sets name  to  the  null  string.   The
                eighth  form is the same as the third form, but make name read-
                only at the same time.
 
                These arguments can be repeated to set  and/or  make  read-only
                multiple  variables  in  a  single set command.  Note, however,
                that variable expansion happens for all  arguments  before  any
                setting  occurs.   Note  also  that ‘=’ can be adjacent to both
                name and word or separated from both by whitespace, but  cannot
                be  adjacent  to  only  one  or  the other.  See also the unset
                builtin command.
 
        setenv [name [value]]
                Without arguments, prints the names and values of all  environ‐
                ment variables.  Given name, sets the environment variable name
                to value or, without value, to the null string.
 
        setpath path (+)
                Equivalent to setpath(1).  (Mach only)
 
        setspath LOCAL|site|cpu ... (+)
                Sets the system execution path.  (TCF only)
 
        settc cap value (+)
                Tells the shell to believe that the terminal capability cap (as
                defined in termcap(5)) has the value value.  No sanity checking
                is done.  Concept terminal users may have to ‘settc xn  no’  to
                get proper wrapping at the rightmost column.
 
        setty [-d|-q|-x] [-a] [[+|-]mode] (+)
                Controls  which  tty  modes (see Terminal management) the shell
                does not allow to change.  -d, -q or -x tells setty to  act  on
                the ‘edit’, ‘quote’ or ‘execute’ set of tty modes respectively;
                without -d, -q or -x, ‘execute’ is used.
 
                Without other arguments, setty lists the modes  in  the  chosen
                set  which are fixed on (‘+mode’) or off (‘-mode’).  The avail‐
                able modes, and thus the display, vary from system  to  system.
                With  -a,  lists all tty modes in the chosen set whether or not
                they are fixed.  With +mode, -mode or mode, fixes  mode  on  or
                off  or removes control from mode in the chosen set.  For exam‐
                ple, ‘setty +echok echoe’ fixes ‘echok’ mode on and allows com‐
                mands  to  turn  ‘echoe’ mode on or off, both when the shell is
                executing commands.
 
        setxvers [string] (+)
                Set the experimental version prefix to string, or removes it if
                string is omitted.  (TCF only)
 
        shift [variable]
                Without  arguments,  discards argv[1] and shifts the members of
                argv to the left.  It is an error for argv not to be set or  to
                have  less than one word as value.  With variable, performs the
                same function on variable.
 
        source [-h] name [args ...]
                The shell reads and executes commands from name.  The  commands
                are  not  placed  on  the history list.  If any args are given,
                they are placed in argv.  (+) source commands may be nested; if
                they  are  nested  too  deeply  the  shell  may run out of file
                descriptors.  An error in a source at any level terminates  all
                nested  source  commands.   With -h, commands are placed on the
                history list instead of being executed, much like ‘history -L’.
 
        stop %job|pid ...
                Stops  the  specified  jobs or processes which are executing in
                the background.  job may be a number, a string, ‘’, ‘%’, ‘+’ or
                ‘-’  as  described under Jobs.  There is no default job; saying
                just ‘stop’ does not stop the current job.
 
        suspend Causes the shell to stop in its tracks, much as if it had  been
                sent  a  stop  signal with ^Z.  This is most often used to stop
                shells started by su(1).
 
        switch (string)
        case str1:
            ...
            breaksw
        ...
        default:
            ...
            breaksw
        endsw   Each case label is successively matched, against the  specified
                string  which is first command and filename expanded.  The file
                metacharacters ‘*’, ‘?’ and ‘[...]’  may be used  in  the  case
                labels,  which  are  variable  expanded.  If none of the labels
                match before a ‘default’ label is  found,  then  the  execution
                begins  after  the  default  label.   Each  case  label and the
                default label must appear at the beginning of a line.  The com‐
                mand  breaksw  causes  execution  to  continue after the endsw.
                Otherwise control may fall  through  case  labels  and  default
                labels  as  in C.  If no label matches and there is no default,
                execution continues after the endsw.
 
        telltc (+)
                Lists the values of all terminal capabilities (see termcap(5)).
 
        time [command]
                Executes command (which must be a simple command, not an alias,
                a pipeline, a command list or a parenthesized command list) and
                prints a time summary as described under the time variable.  If
                necessary, an extra shell is created to print the time  statis‐
                tic when the command completes.  Without command, prints a time
                summary for the current shell and its children.
 
        umask [value]
                Sets the file creation mask to value, which is given in  octal.
                Common  values  for  the mask are 002, giving all access to the
                group and read and execute access to others,  and  022,  giving
                read  and  execute  access  to  the  group and others.  Without
                value, prints the current file creation mask.
 
        unalias pattern
                Removes all aliases whose names  match  pattern.   ‘unalias  *’
                thus removes all aliases.  It is not an error for nothing to be
                unaliased.
 
        uncomplete pattern (+)
                Removes all completions whose names match pattern.  ‘uncomplete
                *’  thus removes all completions.  It is not an error for noth‐
                ing to be uncompleted.
 
        unhash  Disables use of the internal hash table to  speed  location  of
                executed programs.
 
        universe universe (+)
                Sets the universe to universe.  (Masscomp/RTU only)
 
        unlimit [-h] [resource]
                Removes the limitation on resource or, if no resource is speci‐
                fied, all resource limitations.   With  -h,  the  corresponding
                hard limits are removed.  Only the super-user may do this.
 
        unset pattern
                Removes  all  variables  whose names match pattern, unless they
                are read-only.  ‘unset *’ thus  removes  all  variables  unless
                they are read-only; this is a bad idea.  It is not an error for
                nothing to be unset.
 
        unsetenv pattern
                Removes all environment variables whose  names  match  pattern.
                ‘unsetenv  *’ thus removes all environment variables; this is a
                bad idea.  It is not an error for nothing to be unsetenved.
 
        ver [systype [command]] (+)
                Without arguments, prints SYSTYPE.  With systype, sets  SYSTYPE
                to  systype.   With systype and command, executes command under
                systype.  systype may  be  ‘bsd4.3’  or  ‘sys5.3’.   (Domain/OS
                only)
 
        wait    The  shell  waits  for  all  background  jobs.  If the shell is
                interactive, an interrupt will disrupt the wait and  cause  the
                shell  to  print  the  names and job numbers of all outstanding
                jobs.
 
        warp universe (+)
                Sets the universe to universe.  (Convex/OS only)
 
        watchlog (+)
                An alternate name for the log builtin command  (q.v.).   Avail‐
                able  only  if the shell was so compiled; see the version shell
                variable.
 
        where command (+)
                Reports all known  instances  of  command,  including  aliases,
                builtins and executables in path.
 
        which command (+)
                Displays  the  command that will be executed by the shell after
                substitutions, path searching, etc.   The  builtin  command  is
                just  like  which(1), but it correctly reports tcsh aliases and
                builtins and is 10 to 100 times faster.  See  also  the  which-
                command editor command.
 
        while (expr)
        ...
        end     Executes  the  commands  between the while and the matching end
                while expr (an  expression,  as  described  under  Expressions)
                evaluates  non-zero.   while and end must appear alone on their
                input lines.  break and continue may be used  to  terminate  or
                continue the loop prematurely.  If the input is a terminal, the
                user is prompted the first time through the loop as with  fore‐
                ach.
 
    Special aliases (+)
        If  set,  each of these aliases executes automatically at the indicated
        time.  They are all initially undefined.
 
        beepcmd Runs when the shell wants to ring the terminal bell.
 
        cwdcmd  Runs after every change of working directory.  For example,  if
                the  user is working on an X window system using xterm(1) and a
                re-parenting window manager that supports title  bars  such  as
                twm(1) and does
 
                    > alias cwdcmd  ’echo -n "^[]2;${HOST}:$cwd ^G"’
 
                then the shell will change the title of the running xterm(1) to
                be the name of the host, a colon, and the full current  working
                directory.  A fancier way to do that is
 
                    >          alias          cwdcmd          ’echo          -n
                    "^[]2;${HOST}:$cwd^G^[]1;${HOST}^G"’
 
                This will put the hostname and working directory on  the  title
                bar but only the hostname in the icon manager menu.
 
                Note  that  putting  a cd, pushd or popd in cwdcmd may cause an
                infinite loop.  It is the author’s opinion that anyone doing so
                will get what they deserve.
 
        jobcmd  Runs  before  each  command  gets executed, or when the command
                changes state.  This is similar to postcmd,  but  it  does  not
                print builtins.
 
                    > alias jobcmd  ’echo -n "^[]2\;\!#^G"’
 
                then  executing  vi  foo.c  will  put the command string in the
                xterm title bar.
 
        helpcommand
                Invoked by the run-help editor command.  The command  name  for
                which  help is sought is passed as sole argument.  For example,
                if one does
 
                    > alias helpcommand ’\!:1 --help’
 
                then the help display of the command itself  will  be  invoked,
                using  the  GNU help calling convention.  Currently there is no
                easy way to account for various calling conventions (e.g.,  the
                customary Unix ‘-h’), except by using a table of many commands.
 
        periodic
                Runs every tperiod minutes.  This provides a  convenient  means
                for checking on common but infrequent changes such as new mail.
                For example, if one does
 
                    > set tperiod = 30
                    > alias periodic checknews
 
                then the checknews(1) program runs every 30 minutes.  If  peri‐
                odic  is set but tperiod is unset or set to 0, periodic behaves
                like precmd.
 
        precmd  Runs just before each prompt is printed.  For example,  if  one
                does
 
                    > alias precmd date
 
                then  date(1)  runs just before the shell prompts for each com‐
                mand.  There are no limits on what precmd can be set to do, but
                discretion should be used.
 
        postcmd Runs before each command gets executed.
 
                    > alias postcmd  ’echo -n "^[]2\;\!#^G"’
 
                then  executing  vi  foo.c  will  put the command string in the
                xterm title bar.
 
        shell   Specifies the interpreter for executable scripts which  do  not
                themselves  specify an interpreter.  The first word should be a
                full path name to the desired interpreter (e.g., ‘/bin/csh’  or
                ‘/usr/local/bin/tcsh’).
 
    Special shell variables
        The  variables  described  in  this section have special meaning to the
        shell.
 
        The shell sets addsuffix, argv, autologout, command, echo_style,  edit,
        gid,  group, home, loginsh, oid, path, prompt, prompt2, prompt3, shell,
        shlvl, tcsh, term, tty, uid, user and version at startup; they  do  not
        change  thereafter  unless changed by the user.  The shell updates cwd,
        dirstack, owd and status when necessary, and sets logout on logout.
 
        The shell synchronizes afsuser, group, home, path, shlvl, term and user
        with the environment variables of the same names: whenever the environ‐
        ment variable changes the shell changes the corresponding  shell  vari‐
        able  to match (unless the shell variable is read-only) and vice versa.
        Note that although cwd and PWD have identical meanings,  they  are  not
        synchronized in this manner, and that the shell automatically intercon‐
        verts the different formats of path and PATH.
 
        addsuffix (+)
                If set, filename completion adds ‘/’ to the end of  directories
                and  a  space  to the end of normal files when they are matched
                exactly.  Set by default.
 
        afsuser (+)
                If set, autologout’s autolock feature uses its value instead of
                the local username for kerberos authentication.
 
        ampm (+)
                If set, all times are shown in 12-hour AM/PM format.
 
        argv    The  arguments  to  the shell.  Positional parameters are taken
                from argv, i.e., ‘$1’ is replaced by ‘$argv[1]’, etc.   Set  by
                default, but usually empty in interactive shells.
 
        autocorrect (+)
                If  set, the spell-word editor command is invoked automatically
                before each completion attempt.
 
        autoexpand (+)
                If set, the expand-history editor command is invoked  automati‐
                cally before each completion attempt.
 
        autolist (+)
                If set, possibilities are listed after an ambiguous completion.
                If set to ‘ambiguous’, possibilities are listed  only  when  no
                new characters are added by completion.
 
        autologout (+)
                The  first  word  is the number of minutes of inactivity before
                automatic logout.  The optional second word is  the  number  of
                minutes of inactivity before automatic locking.  When the shell
                automatically logs out, it prints ‘auto-logout’, sets the vari‐
                able logout to ‘automatic’ and exits.  When the shell automati‐
                cally locks, the user is required to enter his password to con‐
                tinue  working.   Five  incorrect  attempts result in automatic
                logout.  Set to ‘60’ (automatic logout after 60 minutes, and no
                locking)  by  default in login and superuser shells, but not if
                the shell thinks it is running under a window system (i.e., the
                DISPLAY  environment  variable is set), the tty is a pseudo-tty
                (pty) or the shell was not so compiled (see the  version  shell
                variable).  See also the afsuser and logout shell variables.
 
        backslash_quote (+)
                If set, backslashes (‘\’) always quote ‘\’, ‘’’, and ‘"’.  This
                may make complex quoting tasks easier, but it can cause  syntax
                errors in csh(1) scripts.
 
        catalog The  file  name  of  the  message  catalog.   If  set, tcsh use
                ‘tcsh.${catalog}’ as  a  message  catalog  instead  of  default
                ‘tcsh’.
 
        cdpath  A list of directories in which cd should search for subdirecto‐
                ries if they aren’t found in the current directory.
 
        color   If set, it enables color display for the builtin  ls-F  and  it
                passes  --color=auto  to  ls.   Alternatively, it can be set to
                only ls-F or only ls to enable color to only one command.  Set‐
                ting it to nothing is equivalent to setting it to (ls-F ls).
 
        colorcat
                If set, it enables color escape sequence for NLS message files.
                And display colorful NLS messages.
 
        command (+)
                If set, the command which was passed to the shell with  the  -c
                flag (q.v.).
 
        complete (+)
                If  set to ‘enhance’, completion 1) ignores case and 2) consid‐
                ers periods, hyphens and underscores (‘.’, ‘-’ and ‘_’)  to  be
                word separators and hyphens and underscores to be equivalent.
 
        continue (+)
                If  set  to  a  list  of  commands, the shell will continue the
                listed commands, instead of starting a new one.
 
        continue_args (+)
                Same as continue, but the shell will execute:
 
                    echo ‘pwd‘ $argv > ~/.<cmd>_pause; %<cmd>
 
        correct (+)
                If set to ‘cmd’, commands are automatically spelling-corrected.
                If set to ‘complete’, commands are automatically completed.  If
                set to ‘all’, the entire command line is corrected.
 
        cwd     The full pathname of  the  current  directory.   See  also  the
                dirstack and owd shell variables.
 
        dextract (+)
                If  set,  ‘pushd +n’ extracts the nth directory from the direc‐
                tory stack rather than rotating it to the top.
 
        dirsfile (+)
                The default location in which ‘dirs -S’ and ‘dirs -L’ look  for
                a  history  file.   If unset, ~/.cshdirs is used.  Because only
                ~/.tcshrc  is  normally  sourced  before  ~/.cshdirs,  dirsfile
                should be set in ~/.tcshrc rather than ~/.login.
 
        dirstack (+)
                An  array  of  all  the  directories  on  the  directory stack.
                ‘$dirstack[1]’ is the current working directory, ‘$dirstack[2]’
                the  first  directory on the stack, etc.  Note that the current
                working directory is ‘$dirstack[1]’ but ‘=0’ in directory stack
                substitutions,  etc.   One  can change the stack arbitrarily by
                setting dirstack, but the first element  (the  current  working
                directory)  is  always correct.  See also the cwd and owd shell
                variables.
 
        dspmbyte (+)
                If  set  to  ‘euc’,  it  enables  display  and   editing   EUC-
                kanji(Japanese) code.  If set to ‘sjis’, it enables display and
                editing Shift-JIS(Japanese) code.  If set to ‘big5’, it enables
                display  and  editing Big5(Chinese) code.  If set to ‘utf8’, it
                enables display and editing Utf8(Unicode) code.  If set to  the
                following  format,  it  enables display and editing of original
                multi-byte code format:
 
                    > set dspmbyte = 0000....(256 bytes)....0000
 
                The table requires just 256 bytes.  Each character of 256 char‐
                acters  corresponds  (from  left  to  right) to the ASCII codes
                0x00, 0x01, ... 0xff.  Each character is set  to  number  0,1,2
                and 3.  Each number has the following meaning:
                  0 ... not used for multi-byte characters.
                  1 ... used for the first byte of a multi-byte character.
                  2 ... used for the second byte of a multi-byte character.
                  3  ...  used  for  both  the  first byte and second byte of a
                multi-byte character.
 
                  Example:
                If set to ‘001322’, the first  character  (means  0x00  of  the
                ASCII code) and second character (means 0x01 of ASCII code) are
                set to ‘0’.  Then, it is not used  for  multi-byte  characters.
                The  3rd  character (0x02) is set to ’2’, indicating that it is
                used for the first byte of a  multi-byte  character.   The  4th
                character(0x03) is set ’3’.  It is used for both the first byte
                and the second byte of a multi-byte character.  The 5th and 6th
                characters (0x04,0x05) are set to ’2’, indicating that they are
                used for the second byte of a multi-byte character.
 
                The GNU fileutils version of ls cannot display multi-byte file‐
                names  without  the -N ( --literal ) option.   If you are using
                this version, set the second word of dspmbyte to "ls".  If not,
                for example, "ls-F -l" cannot display multi-byte filenames.
 
                  Note:
                This  variable  can only be used if KANJI and DSPMBYTE has been
                defined at compile time.
 
        dunique (+)
                If set, pushd removes any instances  of  name  from  the  stack
                before pushing it onto the stack.
 
        echo    If  set,  each command with its arguments is echoed just before
                it is executed.  For non-builtin commands all expansions  occur
                before echoing.  Builtin commands are echoed before command and
                filename substitution, because  these  substitutions  are  then
                done selectively.  Set by the -x command line option.
 
        echo_style (+)
                The style of the echo builtin.  May be set to
 
                bsd     Don’t echo a newline if the first argument is ‘-n’.
                sysv    Recognize backslashed escape sequences in echo strings.
                both    Recognize both the ‘-n’  flag  and  backslashed  escape
                        sequences; the default.
                none    Recognize neither.
 
                Set by default to the local system default.  The BSD and System
                V options are described in the echo(1) man pages on the  appro‐
                priate systems.
 
        edit (+)
                If  set,  the  command-line  editor is used.  Set by default in
                interactive shells.
 
        ellipsis (+)
                If set, the ‘%c’/‘%.’ and ‘%C’ prompt sequences (see the prompt
                shell  variable)  indicate skipped directories with an ellipsis
                (‘...’)  instead of ‘/<skipped>’.
 
        fignore (+)
                Lists file name suffixes to be ignored by completion.
 
        filec   In tcsh, completion is always used and this variable is ignored
                by  default. If edit is unset, then the traditional csh comple‐
                tion is used.  If set in csh, filename completion is used.
 
        gid (+) The user’s real group ID.
 
        group (+)
                The user’s group name.
 
        histchars
                A string value determining the characters used in History  sub     
                stitution  (q.v.).  The first character of its value is used as
                the history substitution character, replacing the default char‐
                acter  ‘!’.   The  second  character  of its value replaces the
                character ‘^’ in quick substitutions.
 
        histdup (+)
                Controls handling of duplicate entries in the history list.  If
                set to ‘all’ only unique history events are entered in the his‐
                tory list.  If set to ‘prev’ and the last history event is  the
                same  as  the  current command, then the current command is not
                entered in the history.  If set to ‘erase’ and the  same  event
                is  found  in  the history list, that old event gets erased and
                the current one gets inserted.  Note that the ‘prev’ and  ‘all’
                options renumber history events so there are no gaps.
 
        histfile (+)
                The  default  location  in  which ‘history -S’ and ‘history -L’
                look for a history file.  If unset, ~/.history is used.   hist     
                file  is  useful  when  sharing the same home directory between
                different machines, or when saving separate histories  on  dif‐
                ferent  terminals.   Because only ~/.tcshrc is normally sourced
                before ~/.history, histfile should be set in  ~/.tcshrc  rather
                than ~/.login.
 
        histlit (+)
                If  set, builtin and editor commands and the savehist mechanism
                use the literal (unexpanded) form of lines in the history list.
                See also the toggle-literal-history editor command.
 
        history The  first word indicates the number of history events to save.
                The optional second word (+) indicates the format in which his‐
                tory  is  printed;  if  not given, ‘%h\t%T\t%R\n’ is used.  The
                format sequences are described below  under  prompt;  note  the
                variable meaning of ‘%R’.  Set to ‘100’ by default.
 
        home    Initialized to the home directory of the invoker.  The filename
                expansion of ‘~’ refers to this variable.
 
        ignoreeof
                If set to the empty string or ‘0’ and the  input  device  is  a
                terminal,  the  end-of-file  command  (usually generated by the
                user by typing ‘^D’ on an empty line) causes the shell to print
                ‘Use  "exit" to leave tcsh.’ instead of exiting.  This prevents
                the shell from accidentally being killed.  If set to  a  number
                n,  the  shell ignores n - 1 consecutive end-of-files and exits
                on the nth.  (+) If unset, ‘1’ is used, i.e., the  shell  exits
                on a single ‘^D’.
 
        implicitcd (+)
                If set, the shell treats a directory name typed as a command as
                though it were a request to change to that directory.   If  set
                to  verbose,  the change of directory is echoed to the standard
                output.  This behavior is inhibited  in  non-interactive  shell
                scripts,  or  for  command  strings  with  more  than one word.
                Changing directory takes precedence over executing a like-named
                command,  but  it is done after alias substitutions.  Tilde and
                variable expansions work as expected.
 
        inputmode (+)
                If set to ‘insert’ or ‘overwrite’, puts the  editor  into  that
                input mode at the beginning of each line.
 
        killdup (+)
                Controls  handling  of  duplicate entries in the kill ring.  If
                set to ‘all’ only unique strings are entered in the kill  ring.
                If  set to ‘prev’ and the last killed string is the same as the
                current killed string, then the current string is  not  entered
                in the ring.  If set to ‘erase’ and the same string is found in
                the kill ring, the old string is erased and the current one  is
                inserted.
 
        killring (+)
                Indicates  the number of killed strings to keep in memory.  Set
                to ‘30’ by default.  If unset or set  to  less  than  ‘2’,  the
                shell will only keep the most recently killed string.
 
        listflags (+)
                If  set  to  ‘x’, ‘a’ or ‘A’, or any combination thereof (e.g.,
                ‘xA’), they are used as flags to ls-F, making it act  like  ‘ls
                -xF’,  ‘ls  -Fa’,  ‘ls -FA’ or a combination (e.g., ‘ls -FxA’):
                ‘a’ shows all files (even if they start with a ‘.’), ‘A’  shows
                all  files  but  ‘.’  and ‘..’, and ‘x’ sorts across instead of
                down.  If the second word of listflags is set, it  is  used  as
                the path to ‘ls(1)’.
 
        listjobs (+)
                If set, all jobs are listed when a job is suspended.  If set to
                ‘long’, the listing is in long format.
 
        listlinks (+)
                If set, the ls-F builtin command shows  the  type  of  file  to
                which each symbolic link points.
 
        listmax (+)
                The  maximum number of items which the list-choices editor com‐
                mand will list without asking first.
 
        listmaxrows (+)
                The maximum number of rows of items which the list-choices edi‐
                tor command will list without asking first.
 
        loginsh (+)
                Set  by the shell if it is a login shell.  Setting or unsetting
                it within a shell has no effect.  See also shlvl.
 
        logout (+)
                Set by the shell to ‘normal’ before  a  normal  logout,  ‘auto‐
                matic’  before  an  automatic logout, and ‘hangup’ if the shell
                was killed by a hangup signal (see Signal handling).  See  also
                the autologout shell variable.
 
        mail    The  names  of  the  files or directories to check for incoming
                mail, separated by whitespace, and  optionally  preceded  by  a
                numeric  word.   Before  each prompt, if 10 minutes have passed
                since the last check, the shell checks each file and says  ‘You
                have new mail.’ (or, if mail contains multiple files, ‘You have
                new mail in name.’) if the filesize is  greater  than  zero  in
                size  and has a modification time greater than its access time.
 
                If you are in a login shell, then  no  mail  file  is  reported
                unless  it  has  been  modified  after  the  time the shell has
                started up, to prevent  redundant  notifications.   Most  login
                programs  will  tell  you whether or not you have mail when you
                log in.
 
                If a file specified in mail is  a  directory,  the  shell  will
                count  each  file  within that directory as a separate message,
                and will report ‘You have n mails.’ or ‘You  have  n  mails  in
                name.’  as appropriate.  This functionality is provided primar‐
                ily for those systems which store mail in this manner, such  as
                the Andrew Mail System.
 
                If the first word of mail is numeric it is taken as a different
                mail checking interval, in seconds.
 
                Under very rare circumstances, the shell may report  ‘You  have
                mail.’ instead of ‘You have new mail.’
 
        matchbeep (+)
                If   set  to  ‘never’,  completion  never  beeps.   If  set  to
                ‘nomatch’, it beeps only when there is no  match.   If  set  to
                ‘ambiguous,  it  beeps when there are multiple matches.  If set
                to ‘notunique’, it beeps when there  is  one  exact  and  other
                longer matches.  If unset, ‘ambiguous’ is used.
 
        nobeep (+)
                If  set, beeping is completely disabled.  See also visiblebell.
 
        noclobber
                If set, restrictions are placed on output redirection to insure
                that  files  are not accidentally destroyed and that ‘>>’ redi‐
                rections  refer  to  existing  files,  as  described   in   the
                Input/output section.
 
        noding  If  set,  disable  the  printing  of ‘DING!’ in the prompt time
                specifiers at the change of hour.
 
        noglob  If set, Filename substitution and Directory stack  substitution
                (q.v.)  are  inhibited.   This  is most useful in shell scripts
                which do not deal with filenames, or after a list of  filenames
                has been obtained and further expansions are not desirable.
 
        nokanji (+)
                If  set  and  the  shell  supports Kanji (see the version shell
                variable), it is disabled so that the meta key can be used.
 
        nonomatch
                If set, a Filename substitution or Directory stack substitution
                (q.v.)  which  does  not  match  any  existing  files  is  left
                untouched rather than causing an error.  It is still  an  error
                for  the  substitution  to  be  malformed, e.g., ‘echo [’ still
                gives an error.
 
        nostat (+)
                A list of directories (or glob-patterns  which  match  directo‐
                ries;  see  Filename substitution) that should not be stat(2)ed
                during a completion operation.  This is usually used to exclude
                directories  which  take  too much time to stat(2), for example
                /afs.
 
        notify  If set, the shell  announces  job  completions  asynchronously.
                The  default is to present job completions just before printing
                a prompt.
 
        oid (+) The user’s real organization ID.  (Domain/OS only)
 
        owd (+) The old working directory, equivalent to the ‘-’ used by cd and
                pushd.  See also the cwd and dirstack shell variables.
 
        path    A list of directories in which to look for executable commands.
                A null word specifies the current directory.  If  there  is  no
                path  variable then only full path names will execute.  path is
                set by the shell at startup from the PATH environment  variable
                or, if PATH does not exist, to a system-dependent default some‐
                thing like ‘(/usr/local/bin /usr/bsd /bin  /usr/bin  .)’.   The
                shell  may  put  ‘.’  first or last in path or omit it entirely
                depending on how it was compiled; see the version  shell  vari‐
                able.   A shell which is given neither the -c nor the -t option
                hashes the contents of the directories in  path  after  reading
                ~/.tcshrc  and each time path is reset.  If one adds a new com‐
                mand to a directory in path while the shell is active, one  may
                need to do a rehash for the shell to find it.
 
        printexitvalue (+)
                If set and an interactive program exits with a non-zero status,
                the shell prints ‘Exit status’.
 
        prompt  The string which is printed before reading  each  command  from
                the   terminal.   prompt  may  include  any  of  the  following
                formatting sequences (+),  which  are  replaced  by  the  given
                information:
 
                %/  The current working directory.
                %~  The  current  working directory, but with one’s home direc‐
                    tory represented by ‘~’ and other users’  home  directories
                    represented   by  ‘~user’  as  per  Filename  substitution.
                    ‘~user’ substitution happens only if the shell has  already
                    used ‘~user’ in a pathname in the current session.
                %c[[0]n], %.[[0]n]
                    The trailing component of the current working directory, or
                    n trailing components if a digit n is given.  If  n  begins
                    with  ‘0’,  the  number  of  skipped components precede the
                    trailing component(s) in the  format  ‘/<skipped>trailing’.
                    If  the  ellipsis shell variable is set, skipped components
                    are  represented  by  an  ellipsis  so  the  whole  becomes
                    ‘...trailing’.   ‘~’ substitution is done as in ‘%~’ above,
                    but the ‘~’ component is  ignored  when  counting  trailing
                    components.
                %C  Like %c, but without ‘~’ substitution.
                %h, %!, !
                    The current history event number.
                %M  The full hostname.
                %m  The hostname up to the first ‘.’.
                %S (%s)
                    Start (stop) standout mode.
                %B (%b)
                    Start (stop) boldfacing mode.
                %U (%u)
                    Start (stop) underline mode.
                %t, %@
                    The time of day in 12-hour AM/PM format.
                %T  Like  ‘%t’,  but  in 24-hour format (but see the ampm shell
                    variable).
                %p  The ‘precise’ time of day in  12-hour  AM/PM  format,  with
                    seconds.
                %P  Like  ‘%p’,  but  in 24-hour format (but see the ampm shell
                    variable).
                \c  c is parsed as in bindkey.
                ^c  c is parsed as in bindkey.
                %%  A single ‘%’.
                %n  The user name.
                %j  The number of jobs.
                %d  The weekday in ‘Day’ format.
                %D  The day in ‘dd’ format.
                %w  The month in ‘Mon’ format.
                %W  The month in ‘mm’ format.
                %y  The year in ‘yy’ format.
                %Y  The year in ‘yyyy’ format.
                %l  The shell’s tty.
                %L  Clears from the end of the prompt to end of the display  or
                    the end of the line.
                %$  Expands  the shell or environment variable name immediately
                    after the ‘$’.
                %#  ‘>’ (or the first character of the promptchars shell  vari‐
                    able)  for  normal  users,  ‘#’ (or the second character of
                    promptchars) for the superuser.
                %{string%}
                    Includes string as a literal escape sequence.  It should be
                    used only to change terminal attributes and should not move
                    the cursor location.  This cannot be the last  sequence  in
                    prompt.
                %?  The  return  code  of  the command executed just before the
                    prompt.
                %R  In prompt2, the status of the parser.  In prompt3, the cor‐
                    rected string.  In history, the history string.
 
                ‘%B’,  ‘%S’, ‘%U’ and ‘%{string%}’ are available in only eight-
                bit-clean shells; see the version shell variable.
 
                The bold, standout and underline sequences are  often  used  to
                distinguish a superuser shell.  For example,
 
                    > set prompt = "%m [%h] %B[%@]%b [%/] you rang? "
                    tut [37] [2:54pm] [/usr/accts/sys] you rang? _
 
                If  ‘%t’,  ‘%@’, ‘%T’, ‘%p’, or ‘%P’ is used, and noding is not
                set, then print ‘DING!’ on the change of hour (i.e, ‘:00’  min‐
                utes) instead of the actual time.
 
                Set by default to ‘%# ’ in interactive shells.
 
        prompt2 (+)
                The  string with which to prompt in while and foreach loops and
                after lines ending in ‘\’.  The same format  sequences  may  be
                used  as  in  prompt (q.v.); note the variable meaning of ‘%R’.
                Set by default to ‘%R? ’ in interactive shells.
 
        prompt3 (+)
                The string with  which  to  prompt  when  confirming  automatic
                spelling  correction.  The same format sequences may be used as
                in prompt (q.v.); note the variable meaning of  ‘%R’.   Set  by
                default to ‘CORRECT>%R (y|n|e|a)? ’ in interactive shells.
 
        promptchars (+)
                If  set  (to  a  two-character  string),  the  ‘%#’  formatting
                sequence in the prompt shell  variable  is  replaced  with  the
                first  character  for normal users and the second character for
                the superuser.
 
        pushdtohome (+)
                If set, pushd without arguments does ‘pushd ~’, like cd.
 
        pushdsilent (+)
                If set, pushd and popd do not print the directory stack.
 
        recexact (+)
                If set, completion completes on an exact match even if a longer
                match is possible.
 
        recognize_only_executables (+)
                If  set,  command  listing displays only files in the path that
                are executable.  Slow.
 
        rmstar (+)
                If set, the user is prompted before ‘rm *’ is executed.
 
        rprompt (+)
                The string to print on the right-hand side of the screen (after
                the  command  input)  when the prompt is being displayed on the
                left.  It recognizes the same formatting characters as  prompt.
                It  will  automatically disappear and reappear as necessary, to
                ensure that command input isn’t obscured, and will appear  only
                if  the  prompt, command input, and itself will fit together on
                the first line.  If  edit  isn’t  set,  then  rprompt  will  be
                printed after the prompt and before the command input.
 
        savedirs (+)
                If  set, the shell does ‘dirs -S’ before exiting.  If the first
                word is set to a number, at  most  that  many  directory  stack
                entries are saved.
 
        savehist
                If  set,  the  shell  does ‘history -S’ before exiting.  If the
                first word is set to a number, at  most  that  many  lines  are
                saved.  (The number must be less than or equal to history.)  If
                the second word is set to ‘merge’, the history list  is  merged
                with  the  existing  history  file  instead of replacing it (if
                there is one) and sorted by time  stamp  and  the  most  recent
                events are retained.  (+)
 
        sched (+)
                The  format in which the sched builtin command prints scheduled
                events; if not  given,  ‘%h\t%T\t%R\n’  is  used.   The  format
                sequences  are  described above under prompt; note the variable
                meaning of ‘%R’.
 
        shell   The file in which the shell resides.  This is used  in  forking
                shells  to  interpret  files  which  have execute bits set, but
                which are not executable by the system.  (See  the  description
                of  Builtin and non-builtin command execution.)  Initialized to
                the (system-dependent) home of the shell.
 
        shlvl (+)
                The number of nested shells.  Reset to 1 in login shells.   See
                also loginsh.
 
        status  The  status  returned  by  the  last command.  If it terminated
                abnormally, then 0200 is added to the status.  Builtin commands
                which  fail  return exit status ‘1’, all other builtin commands
                return status ‘0’.
 
        symlinks (+)
                Can be set to several different values to control symbolic link
                (‘symlink’) resolution:
 
                If  set to ‘chase’, whenever the current directory changes to a
                directory containing a symbolic link, it  is  expanded  to  the
                real name of the directory to which the link points.  This does
                not work for the user’s home directory; this is a bug.
 
                If set to ‘ignore’, the shell  tries  to  construct  a  current
                directory relative to the current directory before the link was
                crossed.  This means that cding through  a  symbolic  link  and
                then  ‘cd  ..’ing  returns one to the original directory.  This
                affects only builtin commands and filename completion.
 
                If set to ‘expand’, the shell tries to fix  symbolic  links  by
                actually  expanding arguments which look like path names.  This
                affects any command, not just  builtins.   Unfortunately,  this
                does  not  work  for hard-to-recognize filenames, such as those
                embedded in command options.  Expansion  may  be  prevented  by
                quoting.  While this setting is usually the most convenient, it
                is sometimes misleading and sometimes confusing when  it  fails
                to  recognize  an argument which should be expanded.  A compro‐
                mise is to use ‘ignore’ and use the editor  command  normalize-
                path (bound by default to ^X-n) when necessary.
 
                Some  examples  are  in  order.   First, let’s set up some play
                directories:
 
                    > cd /tmp
                    > mkdir from from/src to
                    > ln -s from/src to/dst
 
                Here’s the behavior with symlinks unset,
 
                    > cd /tmp/to/dst; echo $cwd
                    /tmp/to/dst
                    > cd ..; echo $cwd
                    /tmp/from
 
                here’s the behavior with symlinks set to ‘chase’,
 
                    > cd /tmp/to/dst; echo $cwd
                    /tmp/from/src
                    > cd ..; echo $cwd
                    /tmp/from
 
                here’s the behavior with symlinks set to ‘ignore’,
 
                    > cd /tmp/to/dst; echo $cwd
                    /tmp/to/dst
                    > cd ..; echo $cwd
                    /tmp/to
 
                and here’s the behavior with symlinks set to ‘expand’.
 
                    > cd /tmp/to/dst; echo $cwd
                    /tmp/to/dst
                    > cd ..; echo $cwd
                    /tmp/to
                    > cd /tmp/to/dst; echo $cwd
                    /tmp/to/dst
                    > cd ".."; echo $cwd
                    /tmp/from
                    > /bin/echo ..
                    /tmp/to
                    > /bin/echo ".."
                    ..
 
                Note that ‘expand’ expansion 1) works just  like  ‘ignore’  for
                builtins  like  cd,  2) is prevented by quoting, and 3) happens
                before filenames are passed to non-builtin commands.
 
        tcsh (+)
                The version number of the shell in the format ‘R.VV.PP’,  where
                ‘R’  is  the major release number, ‘VV’ the current version and
                ‘PP’ the patchlevel.
 
        term    The terminal type.  Usually set in ~/.login as described  under
                Startup and shutdown.
 
        time    If set to a number, then the time builtin (q.v.) executes auto‐
                matically after each command which takes more  than  that  many
                CPU seconds.  If there is a second word, it is used as a format
                string for the output of the time builtin.  (u)  The  following
                sequences may be used in the format string:
 
                %U  The time the process spent in user mode in cpu seconds.
                %S  The time the process spent in kernel mode in cpu seconds.
                %E  The elapsed (wall clock) time in seconds.
                %P  The CPU percentage computed as (%U + %S) / %E.
                %W  Number of times the process was swapped.
                %X  The average amount in (shared) text space used in Kbytes.
                %D  The  average  amount in (unshared) data/stack space used in
                    Kbytes.
                %K  The total space used (%X + %D) in Kbytes.
                %M  The maximum memory the process had in use at  any  time  in
                    Kbytes.
                %F  The  number of major page faults (page needed to be brought
                    from disk).
                %R  The number of minor page faults.
                %I  The number of input operations.
                %O  The number of output operations.
                %r  The number of socket messages received.
                %s  The number of socket messages sent.
                %k  The number of signals received.
                %w  The number of voluntary context switches (waits).
                %c  The number of involuntary context switches.
 
                Only the first four sequences are supported on systems  without
                BSD  resource limit functions.  The default time format is ‘%Uu
                %Ss %E %P %X+%Dk %I+%Oio %Fpf+%Ww’  for  systems  that  support
                resource  usage  reporting and ‘%Uu %Ss %E %P’ for systems that
                do not.
 
                Under Sequent’s DYNIX/ptx, %X, %D, %K, %r and %s are not avail‐
                able, but the following additional sequences are:
 
                %Y  The number of system calls performed.
                %Z  The number of pages which are zero-filled on demand.
                %i  The  number  of  times  a  process’s  resident set size was
                    increased by the kernel.
                %d  The number of times  a  process’s  resident  set  size  was
                    decreased by the kernel.
                %l  The number of read system calls performed.
                %m  The number of write system calls performed.
                %p  The number of reads from raw disk devices.
                %q  The number of writes to raw disk devices.
 
                and  the  default  time  format  is  ‘%Uu  %Ss  $E  %P  %I+%Oio
                %Fpf+%Ww’.  Note that the CPU percentage  can  be  higher  than
                100% on multi-processors.
 
        tperiod (+)
                The period, in minutes, between executions of the periodic spe‐
                cial alias.
 
        tty (+) The name of the tty, or empty if not attached to one.
 
        uid (+) The user’s real user ID.
 
        user    The user’s login name.
 
        verbose If set, causes the words of each command to be  printed,  after
                history  substitution  (if  any).   Set  by the -v command line
                option.
 
        version (+)
                The version ID stamp.  It contains the shell’s  version  number
                (see  tcsh), origin, release date, vendor, operating system and
                machine (see VENDOR, OSTYPE and MACHTYPE) and a comma-separated
                list  of options which were set at compile time.  Options which
                are set by default in the distribution are noted.
 
                8b  The shell is eight bit clean; default
                7b  The shell is not eight bit clean
                nls The system’s NLS is used; default for systems with NLS
                lf  Login shells execute /etc/csh.login before instead of after
                    /etc/csh.cshrc   and   ~/.login  before  instead  of  after
                    ~/.tcshrc and ~/.history.
                dl  ‘.’ is put last in path for security; default
                nd  ‘.’ is omitted from path for security
                vi  vi-style editing is the default rather than emacs
                dtr Login shells drop DTR when exiting
                bye bye is a synonym for logout and log is  an  alternate  name
                    for watchlog
                al  autologout is enabled; default
                kan Kanji  is used if appropriate according to locale settings,
                    unless the nokanji shell variable is set
                sm  The system’s malloc(3) is used
                hb  The ‘#!<program> <args>’ convention is emulated  when  exe‐
                    cuting shell scripts
                ng  The newgrp builtin is available
                rh  The  shell attempts to set the REMOTEHOST environment vari‐
                    able
                afs The shell verifies your password with the  kerberos  server
                    if  local authentication fails.  The afsuser shell variable
                    or the AFSUSER environment  variable  override  your  local
                    username if set.
 
                An  administrator may enter additional strings to indicate dif‐
                ferences in the local version.
 
        visiblebell (+)
                If set, a screen flash is used rather than  the  audible  bell.
                See also nobeep.
 
        watch (+)
                A  list of user/terminal pairs to watch for logins and logouts.
                If either the user is ‘any’ all terminals are watched  for  the
                given  user  and  vice  versa.   Setting  watch  to ‘(any any)’
                watches all users and terminals.  For example,
 
                    set watch = (george ttyd1 any console $user any)
 
                reports activity of the user ‘george’ on ttyd1, any user on the
                console, and oneself (or a trespasser) on any terminal.
 
                Logins and logouts are checked every 10 minutes by default, but
                the first word of watch can be set to a number to  check  every
                so many minutes.  For example,
 
                    set watch = (1 any any)
 
                reports any login/logout once every minute.  For the impatient,
                the log builtin command triggers a watch report  at  any  time.
                All  current logins are reported (as with the log builtin) when
                watch is first set.
 
                The who shell variable controls the format of watch reports.
 
        who (+) The format string for watch messages.  The following  sequences
                are replaced by the given information:
 
                %n  The name of the user who logged in/out.
                %a  The  observed  action,  i.e.,  ‘logged on’, ‘logged off’ or
                    ‘replaced olduser on’.
                %l  The terminal (tty) on which the user logged in/out.
                %M  The full hostname of the remote host,  or  ‘local’  if  the
                    login/logout was from the local host.
                %m  The  hostname  of the remote host up to the first ‘.’.  The
                    full name is printed if it is an IP address or an X  Window
                    System display.
 
                %M  and  %m are available on only systems that store the remote
                hostname in /etc/utmp.  If unset, ‘%n has %a %l  from  %m.’  is
                used,  or  ‘%n  has  %a  %l.’  on systems which don’t store the
                remote hostname.
 
        wordchars (+)
                A list of non-alphanumeric characters to be considered part  of
                a  word  by  the  forward-word, backward-word etc., editor com‐
                mands.  If unset, ‘*?_-.[]~=’ is used.
 

ENVIRONMENT

        AFSUSER (+)
                Equivalent to the afsuser shell variable.
 
        COLUMNS The number of columns in the terminal.   See  Terminal  manage     
                ment.
 
        DISPLAY Used by X Window System (see X(1)).  If set, the shell does not
                set autologout (q.v.).
 
        EDITOR  The pathname to a default editor.  See also the VISUAL environ‐
                ment variable and the run-fg-editor editor command.
 
        GROUP (+)
                Equivalent to the group shell variable.
 
        HOME    Equivalent to the home shell variable.
 
        HOST (+)
                Initialized  to  the  name of the machine on which the shell is
                running, as determined by the gethostname(2) system call.
 
        HOSTTYPE (+)
                Initialized to the type of machine on which the shell  is  run‐
                ning, as determined at compile time.  This variable is obsolete
                and will be removed in a future version.
 
        HPATH (+)
                A colon-separated list of directories  in  which  the  run-help
                editor command looks for command documentation.
 
        LANG    Gives the preferred character environment.  See Native Language
                System support.
 
        LC_CTYPE
                If set, only ctype character handling is changed.   See  Native
                Language System support.
 
        LINES   The  number of lines in the terminal.  See Terminal management.
 
        LS_COLORS
                The format of this variable is reminiscent  of  the  termcap(5)
                file  format; a colon-separated list of expressions of the form
                "xx=string", where "xx" is a two-character variable name.   The
                variables with their associated defaults are:
 
                    no   0      Normal (non-filename) text
                    fi   0      Regular file
                    di   01;34  Directory
                    ln   01;36  Symbolic link
                    pi   33     Named pipe (FIFO)
                    so   01;35  Socket
                    do   01;35  Door
                    bd   01;33  Block device
                    cd   01;32  Character device
                    ex   01;32  Executable file
                    mi   (none) Missing file (defaults to fi)
                    or   (none) Orphaned symbolic link (defaults to ln)
                    lc   ^[[    Left code
                    rc   m      Right code
                    ec   (none) End code (replaces lc+no+rc)
 
                You  need to include only the variables you want to change from
                the default.
 
                File names can also be colorized based on  filename  extension.
                This  is  specified  in the LS_COLORS variable using the syntax
                "*ext=string".  For example, using ISO 6429 codes, to color all
                C-language  source files blue you would specify "*.c=34".  This
                would color all files ending in .c in blue (34) color.
 
                Control characters can be  written  either  in  C-style-escaped
                notation,  or  in  stty-like  ^-notation.  The C-style notation
                adds ^[ for Escape, _ for a normal space character, and  ?  for
                Delete.   In  addition,  the ^[ escape character can be used to
                override the default interpretation of ^[, ^, : and =.
 
                Each file will be written as <lc> <color-code> <rc>  <filename>
                <ec>.   If  the  <ec> code is undefined, the sequence <lc> <no>
                <rc> will be used instead.  This is generally  more  convenient
                to  use,  but  less general.  The left, right and end codes are
                provided so you don’t have to type common parts over  and  over
                again  and  to  support weird terminals; you will generally not
                need to change them at all unless your terminal  does  not  use
                ISO 6429 color sequences but a different system.
 
                If your terminal does use ISO 6429 color codes, you can compose
                the type codes (i.e., all except the lc, rc, and ec codes) from
                numerical  commands  separated  by semicolons.  The most common
                commands are:
 
                        0   to restore default color
                        1   for brighter colors
                        4   for underlined text
                        5   for flashing text
                        30  for black foreground
                        31  for red foreground
                        32  for green foreground
                        33  for yellow (or brown) foreground
                        34  for blue foreground
                        35  for purple foreground
                        36  for cyan foreground
                        37  for white (or gray) foreground
                        40  for black background
                        41  for red background
                        42  for green background
                        43  for yellow (or brown) background
                        44  for blue background
                        45  for purple background
                        46  for cyan background
                        47  for white (or gray) background
 
                Not all commands will work on all systems or display devices.
 
                A few terminal programs do not recognize the default  end  code
                properly.   If all text gets colorized after you do a directory
                listing, try changing the no and fi codes from 0 to the numeri‐
                cal codes for your standard fore- and background colors.
 
        MACHTYPE (+)
                The  machine  type  (microprocessor class or machine model), as
                determined at compile time.
 
        NOREBIND (+)
                If set, printable characters are not  rebound  to  self-insert-
                command.  See Native Language System support.
 
        OSTYPE (+)
                The operating system, as determined at compile time.
 
        PATH    A colon-separated list of directories in which to look for exe‐
                cutables.  Equivalent to the path shell variable, but in a dif‐
                ferent format.
 
        PWD (+) Equivalent  to  the cwd shell variable, but not synchronized to
                it; updated only after an actual directory change.
 
        REMOTEHOST (+)
                The host from which the user has logged in remotely, if this is
                the  case  and  the shell is able to determine it.  Set only if
                the shell was so compiled; see the version shell variable.
 
        SHLVL (+)
                Equivalent to the shlvl shell variable.
 
        SYSTYPE (+)
                The current system type.  (Domain/OS only)
 
        TERM    Equivalent to the term shell variable.
 
        TERMCAP The terminal capability string.  See Terminal management.
 
        USER    Equivalent to the user shell variable.
 
        VENDOR (+)
                The vendor, as determined at compile time.
 
        VISUAL  The pathname to a default full-screen  editor.   See  also  the
                EDITOR  environment  variable and the run-fg-editor editor com‐
                mand.
 

FILES

        /etc/csh.cshrc  Read first by every shell.  ConvexOS, Stellix and Intel
                        use  /etc/cshrc  and  NeXTs  use /etc/cshrc.std.  A/UX,
                        AMIX, Cray and IRIX have no equivalent in  csh(1),  but
                        read  this  file  in tcsh anyway.  Solaris 2.x does not
                        have it either, but tcsh reads /etc/.cshrc.  (+)
        /etc/csh.login  Read by login shells after  /etc/csh.cshrc.   ConvexOS,
                        Stellix   and   Intel   use   /etc/login,   NeXTs   use
                        /etc/login.std, Solaris 2.x uses /etc/.login and  A/UX,
                        AMIX, Cray and IRIX use /etc/cshrc.
        ~/.tcshrc (+)   Read by every shell after /etc/csh.cshrc or its equiva‐
                        lent.
        ~/.cshrc        Read by every shell, if ~/.tcshrc doesn’t exist,  after
                        /etc/csh.cshrc  or  its  equivalent.   This manual uses
                        ‘~/.tcshrc’ to mean ‘~/.tcshrc or, if ~/.tcshrc is  not
                        found, ~/.cshrc’.
        ~/.history      Read  by  login  shells  after ~/.tcshrc if savehist is
                        set, but see also histfile.
        ~/.login        Read by login shells  after  ~/.tcshrc  or  ~/.history.
                        The  shell  may  be  compiled  to  read ~/.login before
                        instead of after ~/.tcshrc and ~/.history; see the ver     
                        sion shell variable.
        ~/.cshdirs (+)  Read by login shells after ~/.login if savedirs is set,
                        but see also dirsfile.
        /etc/csh.logout Read by login shells at logout.  ConvexOS, Stellix  and
                        Intel  use  /etc/logout  and NeXTs use /etc/logout.std.
                        A/UX, AMIX, Cray and IRIX have no equivalent in csh(1),
                        but  read  this  file in tcsh anyway.  Solaris 2.x does
                        not have it either, but tcsh reads /etc/.logout.  (+)
        ~/.logout       Read by login shells at logout after /etc/csh.logout or
                        its equivalent.
        /bin/sh         Used  to  interpret  shell  scripts not starting with a
                        ‘#’.
        /tmp/sh*        Temporary file for ‘<<’.
        /etc/passwd     Source of home directories for ‘~name’ substitutions.
 
        The order in which startup files are read may differ if the  shell  was
        so compiled; see Startup and shutdown and the version shell variable.
        This  manual  describes tcsh as a single entity, but experienced csh(1)
        users will want to pay special attention to tcsh’s new features.
 
        A command-line editor, which supports  GNU  Emacs  or  vi(1)-style  key
        bindings.  See The command-line editor and Editor commands.
 
        Programmable,  interactive word completion and listing.  See Completion
        and listing and the complete and uncomplete builtin commands.
 
        Spelling correction (q.v.) of filenames, commands and variables.
 
        Editor commands (q.v.) which perform other useful functions in the mid‐
        dle of typed commands, including documentation lookup (run-help), quick
        editor restarting (run-fg-editor) and  command  resolution  (which-com‐
        mand).
 
        An  enhanced  history  mechanism.  Events in the history list are time-
        stamped.  See also the history command and its associated  shell  vari‐
        ables,  the  previously  undocumented ‘#’ event specifier and new modi‐
        fiers under History substitution, the *-history,  history-search-*,  i-
        search-*,  vi-search-*  and  toggle-literal-history editor commands and
        the histlit shell variable.
 
        Enhanced directory parsing and directory stack handling.  See  the  cd,
        pushd, popd and dirs commands and their associated shell variables, the
        description of Directory stack substitution, the dirstack, owd and sym     
        links shell variables and the normalize-command and normalize-path edi‐
        tor commands.
 
        Negation in glob-patterns.  See Filename substitution.
 
        New File inquiry operators (q.v.) and a  filetest  builtin  which  uses
        them.
 
        A  variety  of  Automatic,  periodic  and timed events (q.v.) including
        scheduled events, special aliases, automatic logout and terminal  lock‐
        ing, command timing and watching for logins and logouts.
 
        Support for the Native Language System (see Native Language System sup     
        port), OS variant features (see OS variant support and  the  echo_style
        shell variable) and system-dependent file locations (see FILES).
 
        Extensive terminal-management capabilities.  See Terminal management.
 
        New  builtin  commands including builtins, hup, ls-F, newgrp, printenv,
        which and where (q.v.).
 
        New variables that make useful  information  easily  available  to  the
        shell.   See  the  gid, loginsh, oid, shlvl, tcsh, tty, uid and version
        shell variables and the HOST, REMOTEHOST, VENDOR, OSTYPE  and  MACHTYPE
        environment variables.
 
        A new syntax for including useful information in the prompt string (see
        prompt).  and special prompts for loops and  spelling  correction  (see
        prompt2 and prompt3).
 
        Read-only variables.  See Variable substitution.
 

BUGS

        When  a  suspended command is restarted, the shell prints the directory
        it started in if this is different from the  current  directory.   This
        can be misleading (i.e., wrong) as the job may have changed directories
        internally.
 
        Shell  builtin  functions  are  not   stoppable/restartable.    Command
        sequences  of the form ‘a ; b ; c’ are also not handled gracefully when
        stopping is attempted.  If you suspend ‘b’, the shell will then immedi‐
        ately  execute  ‘c’.   This  is especially noticeable if this expansion
        results from an alias.  It suffices to place the sequence  of  commands
        in ()’s to force it to a subshell, i.e., ‘( a ; b ; c )’.
 
        Control  over tty output after processes are started is primitive; per‐
        haps this will inspire someone to  work  on  a  good  virtual  terminal
        interface.   In  a  virtual  terminal  interface  much more interesting
        things could be done with output control.
 
        Alias substitution is most often used to clumsily simulate shell proce‐
        dures; shell procedures should be provided rather than aliases.
 
        Commands  within  loops  are  not  placed in the history list.  Control
        structures should be parsed rather than being  recognized  as  built-in
        commands.   This would allow control commands to be placed anywhere, to
        be combined with ‘|’, and to be used with ‘&’ and ‘;’ metasyntax.
 
        foreach doesn’t ignore here documents when looking for its end.
 
        It should be possible to use the ‘:’ modifiers on the output of command
        substitutions.
 
        The  screen  update for lines longer than the screen width is very poor
        if the terminal cannot move the cursor up (i.e., terminal type ‘dumb’).
 
        HPATH and NOREBIND don’t need to be environment variables.
 
        Glob-patterns  which  do  not use ‘?’, ‘*’ or ‘[]’ or which use ‘{}’ or
        ‘~’ are not negated correctly.
 
        The single-command form of if  does  output  redirection  even  if  the
        expression is false and the command is not executed.
 
        ls-F includes file identification characters when sorting filenames and
        does not handle control characters in filenames  well.   It  cannot  be
        interrupted.
 
        Report bugs to tcsh-bugs@mx.gw.com, preferably with fixes.  If you want
        to help maintain and test tcsh, send mail  to  listserv@mx.gw.com  with
        the  text ‘subscribe tcsh <your name>’ on a line by itself in the body.
        You can also ‘subscribe tcsh-bugs <your name>’ to get all bug  reports,
        or  ‘subscribe tcsh-diffs <your name>’ to get the development list plus
        diffs for each patchlevel.
        In 1964, DEC produced the PDP-6.  The PDP-10 was a later re-implementa‐
        tion.   It  was  re-christened  the DECsystem-10 in 1970 or so when DEC
        brought out the second model, the KI10.
 
        TENEX was created at Bolt, Beranek & Newman (a Cambridge, Massachusetts
        think  tank)  in  1972  as an experiment in demand-paged virtual memory
        operating systems.  They built a new pager for the DEC PDP-10 and  cre‐
        ated the OS to go with it.  It was extremely successful in academia.
 
        In  1975,  DEC  brought  out  a new model of the PDP-10, the KL10; they
        intended to have only a version of TENEX, which they had licensed  from
        BBN,  for  the new box.  They called their version TOPS-20 (their capi‐
        talization is trademarked).  A lot of  TOPS-10  users  (‘The  OPerating
        System  for PDP-10’) objected; thus DEC found themselves supporting two
        incompatible systems on the same hardware--but then there were 6 on the
        PDP-11!
 
        TENEX,  and  TOPS-20  to  version 3, had command completion via a user-
        code-level subroutine library called ULTCMD.  With version 3, DEC moved
        all  that  capability  and more into the monitor (‘kernel’ for you Unix
        types), accessed by the COMND% JSYS (‘Jump to SYStem’ instruction,  the
        supervisor call mechanism [are my IBM roots also showing?]).
 
        The creator of tcsh was impressed by this feature and several others of
        TENEX and TOPS-20, and created a version of csh which mimicked them.
 

LIMITATIONS

        Words can be no longer than 1024 characters.
 
        The system limits argument lists to 10240 characters.
 
        The number of arguments to a command which involves filename  expansion
        is  limited  to  1/6th  the number of characters allowed in an argument
        list.
 
        Command substitutions  may  substitute  no  more  characters  than  are
        allowed in an argument list.
 
        To  detect  looping,  the shell restricts the number of alias substitu‐
        tions on a single line to 20.
        csh(1), emacs(1), ls(1), newgrp(1), sh(1), setpath(1), stty(1),  su(1),
        tset(1),   vi(1),   x(1),  access(2),  execve(2),  fork(2),  killpg(2),
        pipe(2), setrlimit(2), sigvec(2), stat(2), umask(2), vfork(2), wait(2),
        malloc(3),  setlocale(3),  tty(4),  a.out(5),  termcap(5),  environ(7),
        termio(7), Introduction to the C Shell
 

VERSION

        This manual documents tcsh 6.12.00 (Astron) 2002-07-23.
 

AUTHORS

        William Joy
          Original author of csh(1)
        J.E. Kulp, IIASA, Laxenburg, Austria
          Job control and directory stack features
        Ken Greer, HP Labs, 1981
          File name completion
        Mike Ellis, Fairchild, 1983
          Command name recognition/completion
        Paul Placeway, Ohio State CIS Dept., 1983-1993
          Command line editor, prompt routines, new glob  syntax  and  numerous
          fixes and speedups
        Karl Kleinpaste, CCI 1983-4
          Special  aliases,  directory  stack  extraction  stuff,  login/logout
          watch, scheduled events, and the idea of the new prompt format
        Rayan Zachariassen, University of Toronto, 1984
          ls-F and which builtins and numerous  bug  fixes,  modifications  and
          speedups
        Chris Kingsley, Caltech
          Fast storage allocator routines
        Chris Grevstad, TRW, 1987
          Incorporated 4.3BSD csh into tcsh
        Christos S. Zoulas, Cornell U. EE Dept., 1987-94
          Ports   to   HPUX,   SVR2  and  SVR3,  a  SysV  version  of  getwd.c,
          SHORT_STRINGS support and a new version of sh.glob.c
        James J Dempsey, BBN, and Paul Placeway, OSU, 1988
          A/UX port
        Daniel Long, NNSC, 1988
          wordchars
        Patrick Wolfe, Kuck and Associates, Inc., 1988
          vi mode cleanup
        David C Lawrence, Rensselaer Polytechnic Institute, 1989
          autolist and ambiguous completion listing
        Alec Wolman, DEC, 1989
          Newlines in the prompt
        Matt Landau, BBN, 1989
          ~/.tcshrc
        Ray Moody, Purdue Physics, 1989
          Magic space bar history expansion
        Mordechai ????, Intel, 1989
          printprompt() fixes and additions
        Kazuhiro Honda, Dept. of Computer Science, Keio University, 1989
          Automatic spelling correction and prompt3
        Per Hedeland, Ellemtel, Sweden, 1990-
          Various bugfixes, improvements and manual updates
        Hans J. Albertsson (Sun Sweden)
          ampm, settc and telltc
        Michael Bloom
          Interrupt handling fixes
        Michael Fine, Digital Equipment Corp
          Extended key support
        Eric Schnoebelen, Convex, 1990
          Convex support, lots of csh bug fixes, save and restore of  directory
          stack
        Ron Flax, Apple, 1990
          A/UX 2.0 (re)port
        Dan Oscarsson, LTH Sweden, 1990
          NLS support and simulated NLS support for non NLS sites, fixes
        Johan Widen, SICS Sweden, 1990
          shlvl, Mach support, correct-line, 8-bit printing
        Matt Day, Sanyo Icon, 1990
          POSIX termio support, SysV limit fixes
        Jaap Vermeulen, Sequent, 1990-91
          Vi mode fixes, expand-line, window change fixes, Symmetry port
        Martin Boyer, Institut de recherche d’Hydro-Quebec, 1991
          autolist  beeping  options, modified the history search to search for
          the whole string from the beginning of the line to the cursor.
        Scott Krotz, Motorola, 1991
          Minix port
        David Dawes, Sydney U. Australia, Physics Dept., 1991
          SVR4 job control fixes
        Jose Sousa, Interactive Systems Corp., 1991
          Extended vi fixes and vi delete command
        Marc Horowitz, MIT, 1991
          ANSIfication fixes, new exec hashing code, imake fixes, where
        Bruce Sterling Woodcock, sterling@netcom.com, 1991-1995
          ETA and Pyramid port, Makefile and lint fixes, ignoreeof=n  addition,
          and various other portability changes and bug fixes
        Jeff Fink, 1992
          complete-word-fwd and complete-word-back
        Harry C. Pulley, 1992
          Coherent port
        Andy Phillips, Mullard Space Science Lab U.K., 1992
          VMS-POSIX port
        Beto Appleton, IBM Corp., 1992
          Walking  process  group fixes, csh bug fixes, POSIX file tests, POSIX
          SIGHUP
        Scott Bolte, Cray Computer Corp., 1992
          CSOS port
        Kaveh R. Ghazi, Rutgers University, 1992
          Tek, m88k, Titan and Masscomp ports and fixes.  Added  autoconf  sup‐
          port.
        Mark Linderman, Cornell University, 1992
          OS/2 port
        Mika Liljeberg, liljeber@kruuna.Helsinki.FI, 1992
          Linux port
        Tim P. Starrin, NASA Langley Research Center Operations, 1993
          Read-only variables
        Dave Schweisguth, Yale University, 1993-4
          New man page and tcsh.man2html
        Larry Schwimmer, Stanford University, 1993
          AFS and HESIOD patches
        Luke Mewburn, RMIT University, 1994-6
          Enhanced directory printing in prompt, added ellipsis and rprompt.
        Edward Hutchins, Silicon Graphics Inc., 1996
          Added implicit cd.
        Martin Kraemer, 1997
          Ported to Siemens Nixdorf EBCDIC machine
        Amol Deshpande, Microsoft, 1997
          Ported  to  WIN32  (Windows/95 and Windows/NT); wrote all the missing
          library and message catalog code to interface to Windows.
        Taga Nayuta, 1998
          Color ls additions.
        Bryan Dunlap, Clayton Elwell, Karl Kleinpaste, Bob Manson, Steve Romig,
        Diana  Smetters, Bob Sutterfield, Mark Verber, Elizabeth Zwicky and all
        the other people at Ohio State for suggestions and encouragement
 
        All the people on the net, for putting up with, reporting bugs in,  and
        suggesting new additions to each and every version
 
        Richard M. Alderson III, for writing the ‘T in tcsh’ section
 

Sections

Based on BSD UNIX
FreeBSD is an advanced operating system for x86 compatible (including Pentium and Athlon), amd64 compatible (including Opteron, Athlon64, and EM64T), UltraSPARC, IA-64, PC-98 and ARM architectures. It is derived from BSD, the version of UNIX developed at the University of California, Berkeley. It is developed and maintained by a large team of individuals. Additional platforms are in various stages of development.