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GREP(1)								       GREP(1)

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

SYNOPOSIS
       grep [ -[[AB] ]num ] [ -[CEFGVBchilnsvwx] ] [ -e	] pattern | -ffile ] [
       files...	 ]

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.

       There are three major variants of grep,	controlled  by	the  following
       options.
       -G     Interpret	 pattern  as  a	 basic regular expression (see below).
	      This is the default.
       -E     Interpret	pattern	as an extended regular expression (see below).
       -F     Interpret	 pattern as a list of fixed strings, separated by new-
	      lines, any of which is to	be matched.
       In addition, two	variant	programs egrep and fgrep are available.	 Egrep
       is  similiar (but not identical)	to grep	-E, and	is compatible with the
       historical Unix egrep.  Fgrep is	the same as grep -F.

       All variants of grep understand the following options:
       -num   Matches will be printed with num lines of	leading	 and  trailing
	      context.	 However,  grep	 will  never print any given line more
	      than once.
       -A num Print num	lines of trailing context after	matching lines.
       -B num Print num	lines of leading context before	matching lines.
       -C     Equivalent to -2.
       -V     Print the	version	number of grep to standard error.   This  ver-
	      sion number should be included in	all bug	reports	(see below).
       -b     Print  the byte offset within the	input file before each line of
	      output.
       -c     Suppress normal output; instead print a count of matching	 lines
	      for each input file.  With the -v	option (see below), count non-
	      matching lines.
       -e pattern
	      Use pattern as the pattern; useful to protect patterns beginning
	      with -.
       -f file
	      Obtain the pattern from file.
       -h     Suppress	the  prefixing	of  filenames  on output when multiple
	      files are	searched.
       -i     Ignore case distinctions in  both	 the  pattern  and  the	 input
	      files.
       -L     Suppress	normal	output;	 instead  print	the name of each input
	      file from	which no output	would normally have been printed.
       -l     Suppress normal output; instead print the	 name  of  each	 input
	      file from	which output would normally have been printed.
       -n     Prefix each line of output with the line number within its input
	      file.
       -q     Quiet; suppress normal output.
       -s     Suppress error messages about nonexistent	or unreadable files.
       -v     Invert the sense of matching, to select non-matching lines.
       -w     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     Select only those	matches	that exactly match the whole line.

REGULAR	EXPRESSIONS
       A regular expression is a pattern that  describes  a  set  of  strings.
       Regular	expressions  are constructed analagously 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
       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 ASCII
       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	 exam-
       ple, [[:alnum:]]	means [0-9A-Za-z], except the latter form is dependent
       upon the	ASCII character	encoding,  whereas  the	 former	 is  portable.
       (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 matching a single character	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.
       {,m}   The preceding item is optional and is matched at most m 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 \?,
       \+, \{, \|, \(, and \).

       In egrep	the metacharacter { loses its special meaning; instead use \{.

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@prep.ai.mit.edu.  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		       1992 September 10		       GREP(1)

NAME | SYNOPOSIS | DESCRIPTION | REGULAR EXPRESSIONS | DIAGNOSTICS | BUGS

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