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GREP(1)

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NAME    [Toc]    [Back]

       grep,  egrep,  fgrep, zgrep, zegrep, zfgrep, bzgrep, bzegrep, bzfgrep -
       print lines matching a pattern

SYNOPSIS    [Toc]    [Back]

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

DESCRIPTION    [Toc]    [Back]

       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.  zegrep is the same as grep -EZ.  zfgrep is  the  same
       as grep -FZ.

OPTIONS    [Toc]    [Back]

       -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 message
 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 terminal
 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, directories
 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  newlines,
 any of which is to be matched.

       -f FILE, --file=FILE
	      Obtain  patterns	from  FILE, one per line.  The empty file contains
 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 equivalent
 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 conform
 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  MSWindows,
	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-Windows.


       -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 version
 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  constituent
	character.  Similarly, it must be either at the end of
	      the line or followed by a non-word constituent character.  Wordconstituent
  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.

       -J, --bz2decompress
	      Decompress the bzip2(1) compressed input data before  searching.

REGULAR EXPRESSIONS    [Toc]    [Back]

       A  regular  expression  is  a  pattern that describes a set of strings.
       Regular expressions are constructed analogously to  arithmetic  expressions,
 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	available
  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  characters
  may  be  specified by giving the first and last characters, separated
 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 operators:

       ?      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 subexpression.


       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 regular
 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 specification.
  For example, the shell command egrep '{1' searches for the  twocharacter
  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    [Toc]    [Back]

       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 determined
 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    [Toc]    [Back]
	      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    [Toc]    [Back]

       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, inaccessible
 input files, or other system errors.

BUGS    [Toc]    [Back]

       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			  2000/01/26			       GREP(1)
[ Back ]
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