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GREP(1)								       GREP(1)

NAME
       grep, egrep, fgrep - 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.

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 therefore 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 platforms 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.

       -Z, --null
	      Output  a	 zero  byte  (the  ASCII NUL character) instead of the
	      character that normally follows a file name.  For example,  grep
	      -lZ  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.

REGULAR EXPRESSIONS
       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.

ENVIRONMENT VARIABLES
       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”.   POSIXLY_CORRECT	also  disables	 _N_GNU_nonop‐
	      tion_argv_flags_, described below.

       _N_GNU_nonoption_argv_flags_
	      (Here  N is grep's numeric process ID.)  If the ith character of
	      this environment variable's value is 1, do not consider the  ith
	      operand  of  grep to be an option, even if it appears to be one.
	      A shell can put this variable in the environment for  each  com‐
	      mand  it runs, specifying which operands are the results of file
	      name wildcard expansion and therefore should not be  treated  as
	      options.	 This  behavior	 is  available	only  with  the	 GNU C
	      library, and only when POSIXLY_CORRECT is not set.

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.

GNU Project			  2002/04/30			       GREP(1)
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