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grep, egrep, fgrep, zgrep - print lines matching a pattern

 

NAME

        grep, egrep, fgrep, zgrep - print lines matching a pattern
 

SYNOPSIS

        grep [options] PATTERN [FILE...]
        grep [options] [-e PATTERN | -f FILE] [FILE...]
 

DESCRIPTION

        grep  searches the named input FILEs (or standard input if no files are
        named, or the file name - is given) for lines containing a match to the
        given PATTERN.  By default, grep prints the matching lines.
 
        In addition, two variant programs egrep and fgrep are available.  egrep
        is the same as grep -E.  fgrep is the same as grep -F.   zgrep  is  the
        same as grep -Z.
 

OPTIONS

        -A NUM, --after-context=NUM
               Print NUM lines of trailing context after matching lines.
 
        -a, --text
               Process  a binary file as if it were text; this is equivalent to
               the --binary-files=text option.
 
        -B NUM, --before-context=NUM
               Print NUM lines of leading context before matching lines.
 
        -C [NUM], -NUM, --context[=NUM]
               Print NUM lines (default 2) of output context.
 
        -b, --byte-offset
               Print the byte offset within the input file before each line  of
               output.
 
        --binary-files=TYPE
               If the first few bytes of a file indicate that the file contains
               binary data, assume that the file is of type TYPE.  By  default,
               TYPE is binary, and grep normally outputs either a one-line mes‐
               sage saying that a binary file matches, or no message  if  there
               is  no  match.   If  TYPE  is without-match, grep assumes that a
               binary file does not match; this is equivalent to the -I option.
               If  TYPE  is  text,  grep  processes a binary file as if it were
               text; this is  equivalent  to  the  -a  option.   Warning:  grep
               --binary-files=text  might output binary garbage, which can have
               nasty side effects if the output is a terminal and if the termi‐
               nal driver interprets some of it as commands.
 
        -c, --count
               Suppress  normal output; instead print a count of matching lines
               for each input file.  With the -v,  --invert-match  option  (see
               below), count non-matching lines.
 
        -d ACTION, --directories=ACTION
               If  an  input file is a directory, use ACTION to process it.  By
               default, ACTION is read, which means that directories  are  read
               just  as if they were ordinary files.  If ACTION is skip, direc‐
               tories are silently skipped.  If ACTION is recurse,  grep  reads
               all  files under each directory, recursively; this is equivalent
               to the -r option.
 
        -E, --extended-regexp
               Interpret PATTERN as an extended regular expression (see below).
 
        -e PATTERN, --regexp=PATTERN
               Use PATTERN as the pattern; useful to protect patterns beginning
               with -.
 
        -F, --fixed-strings
               Interpret PATTERN as a list of fixed strings, separated by  new‐
               lines, any of which is to be matched.
 
        -f FILE, --file=FILE
               Obtain  patterns  from  FILE, one per line.  The empty file con‐
               tains zero patterns, and therfore matches nothing.
 
        -G, --basic-regexp
               Interpret PATTERN as a basic  regular  expression  (see  below).
               This is the default.
 
        -H, --with-filename
               Print the filename for each match.
 
        -h, --no-filename
               Suppress  the  prefixing  of  filenames  on output when multiple
               files are searched.
 
        --help Output a brief help message.
 
        -I     Process a binary file as if it did not  contain  matching  data;
               this is equivalent to the --binary-files=without-match option.
 
        -i, --ignore-case
               Ignore  case  distinctions  in  both  the  PATTERN and the input
               files.
 
        -L, --files-without-match
               Suppress normal output; instead print the  name  of  each  input
               file from which no output would normally have been printed.  The
               scanning will stop on the first match.
 
        -l, --files-with-matches
               Suppress normal output; instead print the  name  of  each  input
               file  from  which  output would normally have been printed.  The
               scanning will stop on the first match.
 
        --mmap If possible, use the mmap(2) system call to read input,  instead
               of  the default read(2) system call.  In some situations, --mmap
               yields better performance.  However, --mmap can cause  undefined
               behavior  (including  core dumps) if an input file shrinks while
               grep is operating, or if an I/O error occurs.
 
        -n, --line-number
               Prefix each line of output with the line number within its input
               file.
 
        -q, --quiet, --silent
               Quiet;  suppress  normal  output.  The scanning will stop on the
               first match.  Also see the -s or --no-messages option below.
 
        -r, --recursive
               Read all files under each directory, recursively; this is equiv‐
               alent to the -d recurse option.
 
        -s, --no-messages
               Suppress  error  messages about nonexistent or unreadable files.
               Portability note: unlike GNU grep, traditional grep did not con‐
               form to POSIX.2, because traditional grep lacked a -q option and
               its -s option behaved like GNU grep’s -q option.  Shell  scripts
               intended to be portable to traditional grep should avoid both -q
               and -s and should redirect output to /dev/null instead.
 
        -U, --binary
               Treat the file(s) as binary.  By default, under MS-DOS  and  MS-
               Windows,  grep  guesses the file type by looking at the contents
               of the first 32KB read from the file.  If grep decides the  file
               is  a  text  file, it strips the CR characters from the original
               file contents (to make regular expressions with  ^  and  $  work
               correctly).  Specifying -U overrules this guesswork, causing all
               files to be read and passed to the matching mechanism  verbatim;
               if  the  file is a text file with CR/LF pairs at the end of each
               line, this will cause some regular expressions  to  fail.   This
               option  has no effect on platforms other than MS-DOS and MS-Win‐
               dows.
 
        -u, --unix-byte-offsets
               Report Unix-style byte offsets.   This  switch  causes  grep  to
               report  byte  offsets  as if the file were Unix-style text file,
               i.e. with CR characters stripped off.  This will produce results
               identical to running grep on a Unix machine.  This option has no
               effect unless -b option is also used; it has no effect on  plat‐
               forms other than MS-DOS and MS-Windows.
 
        -V, --version
               Print  the  version number of grep to standard error.  This ver‐
               sion number should be included in all bug reports (see below).
 
        -v, --invert-match
               Invert the sense of matching, to select non-matching lines.
 
        -w, --word-regexp
               Select only those  lines  containing  matches  that  form  whole
               words.   The  test is that the matching substring must either be
               at the beginning of the line, or preceded  by  a  non-word  con‐
               stituent  character.  Similarly, it must be either at the end of
               the line or followed by a non-word constituent character.  Word-
               constituent  characters are letters, digits, and the underscore.
 
        -x, --line-regexp
               Select only those matches that exactly match the whole line.
 
        -y     Obsolete synonym for -i.
 
        --null Output a zero byte (the ASCII  NUL  character)  instead  of  the
               character  that normally follows a file name.  For example, grep
               -l --null outputs a zero byte after each file  name  instead  of
               the  usual  newline.   This option makes the output unambiguous,
               even in the presence of file names containing unusual characters
               like  newlines.  This option can be used with commands like find
               -print0, perl -0, sort -z, and xargs  -0  to  process  arbitrary
               file names, even those that contain newline characters.
 
        -Z, --decompress
               Decompress the input data before searching.  This option is only
               available if compiled with zlib(3) library.
        A regular expression is a pattern that  describes  a  set  of  strings.
        Regular  expressions  are constructed analogously to arithmetic expres‐
        sions, by using various operators to combine smaller expressions.
 
        grep understands two different versions of regular  expression  syntax:
        “basic”  and “extended.”  In GNU grep, there is no difference in avail‐
        able functionality using  either  syntax.   In  other  implementations,
        basic regular expressions are less powerful.  The following description
        applies to extended regular expressions; differences for basic  regular
        expressions are summarized afterwards.
 
        The  fundamental building blocks are the regular expressions that match
        a single character.  Most characters, including all letters and digits,
        are  regular expressions that match themselves.  Any metacharacter with
        special meaning may be quoted by preceding it with a backslash.
 
        A list of characters enclosed by [ and ] matches any  single  character
        in that list; if the first character of the list is the caret ^ then it
        matches any character not  in  the  list.   For  example,  the  regular
        expression  [0123456789]  matches any single digit.  A range of charac‐
        ters may be specified by giving the first and  last  characters,  sepa‐
        rated  by  a  hyphen.  Finally, certain named classes of characters are
        predefined.  Their names are self explanatory, and they are  [:alnum:],
        [:alpha:],   [:cntrl:],  [:digit:],  [:graph:],  [:lower:],  [:print:],
        [:punct:],  [:space:],  [:upper:],  and   [:xdigit:].    For   example,
        [[:alnum:]]  means [0-9A-Za-z], except the latter form depends upon the
        POSIX locale and the ASCII character encoding, whereas  the  former  is
        independent  of  locale  and character set.  (Note that the brackets in
        these class names are part of the symbolic names, and must be  included
        in  addition  to  the  brackets  delimiting  the  bracket  list.)  Most
        metacharacters lose their special meaning inside lists.  To  include  a
        literal  ] place it first in the list.  Similarly, to include a literal
        ^ place it anywhere but first.  Finally, to include a literal  -  place
        it last.
 
        The period .  matches any single character.  The symbol \w is a synonym
        for [[:alnum:]] and \W is a synonym for [^[:alnum]].
 
        The caret ^ and the dollar sign $ are metacharacters that  respectively
        match the empty string at the beginning and end of a line.  The symbols
        \< and \> respectively match the empty string at the beginning and  end
        of  a  word.   The  symbol \b matches the empty string at the edge of a
        word, and \B matches the empty string provided it’s not at the edge  of
        a word.
 
        A regular expression may be followed by one of several repetition oper‐
        ators:
        ?      The preceding item is optional and matched at most once.
        *      The preceding item will be matched zero or more times.
        +      The preceding item will be matched one or more times.
        {n}    The preceding item is matched exactly n times.
        {n,}   The preceding item is matched n or more times.
        {n,m}  The preceding item is matched at least n  times,  but  not  more
               than m times.
 
        Two  regular  expressions  may  be  concatenated; the resulting regular
        expression matches any string formed by  concatenating  two  substrings
        that respectively match the concatenated subexpressions.
 
        Two  regular  expressions  may  be  joined by the infix operator |; the
        resulting regular expression matches any string matching either  subex‐
        pression.
 
        Repetition  takes  precedence  over  concatenation, which in turn takes
        precedence over alternation.  A whole subexpression may be enclosed  in
        parentheses to override these precedence rules.
 
        The  backreference \n, where n is a single digit, matches the substring
        previously matched by the nth parenthesized subexpression of the  regu‐
        lar expression.
 
        In  basic  regular  expressions the metacharacters ?, +, {, |, (, and )
        lose their special meaning; instead use the  backslashed  versions  \?,
        \+, \{, \|, \(, and \).
 
        Traditional  egrep  did not support the { metacharacter, and some egrep
        implementations support \{ instead, so portable scripts should avoid  {
        in egrep patterns and should use [{] to match a literal {.
 
        GNU  egrep  attempts to support traditional usage by assuming that { is
        not special if it would be the start of an invalid interval  specifica‐
        tion.   For example, the shell command egrep      {1      searches for the two-
        character string {1 instead of reporting a syntax error in the  regular
        expression.  POSIX.2 allows this behavior as an extension, but portable
        scripts should avoid it.
        GREP_OPTIONS
               This variable specifies default options to be placed in front of
               any   explicit   options.    For  example,  if  GREP_OPTIONS  is
                    --binary-files=without-match --directories=skip     , grep  behaves
               as  if the two options --binary-files=without-match and --direc     
               tories=skip had been  specified  before  any  explicit  options.
               Option  specifications are separated by whitespace.  A backslash
               escapes the next character, so it can  be  used  to  specify  an
               option containing whitespace or a backslash.
 
        LC_ALL, LC_MESSAGES, LANG
               These variables specify the LC_MESSAGES locale, which determines
               the language that grep uses for messages.  The locale is  deter‐
               mined  by  the  first  of these variables that is set.  American
               English is used if none of these environment variables are  set,
               or  if  the message catalog is not installed, or if grep was not
               compiled with national language support (NLS).
 
        LC_ALL, LC_CTYPE, LANG
               These variables specify the LC_CTYPE  locale,  which  determines
               the  type  of characters, e.g., which characters are whitespace.
               The locale is determined by the first of these variables that is
               set.   The  POSIX  locale  is  used if none of these environment
               variables are set, or if the locale catalog is not installed, or
               if grep was not compiled with national language support (NLS).
 
        POSIXLY_CORRECT
               If  set,  grep  behaves  as  POSIX.2  requires;  otherwise, grep
               behaves more like other GNU  programs.   POSIX.2  requires  that
               options that follow file names must be treated as file names; by
               default, such options are permuted to the front of  the  operand
               list  and  are  treated as options.  Also, POSIX.2 requires that
               unrecognized options be diagnosed as “illegal”, but  since  they
               are  not  really against the law the default is to diagnose them
               as “invalid”.
 

DIAGNOSTICS

        Normally, exit status is 0 if matches were found, and 1 if  no  matches
        were  found.   (The  -v  option  inverts the sense of the exit status.)
        Exit status is 2 if there were syntax errors in the pattern, inaccessi‐
        ble input files, or other system errors.
 

BUGS

        Email  bug  reports  to  bug-gnu-utils@gnu.org.  Be sure to include the
        word “grep” somewhere in the “Subject:” field.
 
        Large repetition counts in the {m,n} construct may cause  grep  to  use
        lots of memory.  In addition, certain other obscure regular expressions
        require exponential time and space, and may cause grep to  run  out  of
        memory.
 
        Backreferences are very slow, and may require exponential time.
 

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