1988 December 13 GNU Project 

grep, egrep - print lines matching a regular expression

grep [-CVbchilnsvwx] [- num] [-AB num] [ [-e] expr | -f file ] [ "files ..." ]

DESCRIPTION

Grep searches the files listed in the arguments (or standard
input if no files are given) for all lines that contain a match for
the given expr . If any lines match, they are printed. 
Also, if any matches were found, grep exits with a status of 0, but 
if no matches were found it exits with a status of 1.  This is useful 
for building shell scripts that use grep as a condition for, for
example, the if statement.

When invoked as egrep the syntax of the expr is slightly different; 
See below.

"REGULAR EXPRESSIONS"

(grep)	(egrep)		(explanation)
a single (non-meta) character matches itself.
.       .       	matches any single character except newline.
\?	?	        postfix operator; preceeding item is optional.
*	*       	postfix operator; preceeding item 0 or more times.
\+	+	        postfix operator; preceeding item 1 or more times.
\|	|	        infix operator; matches either argument.
^	^	        matches the empty string at the beginning of a line.
$	$	        matches the empty string at the end of a line.
\<	\<       	matches the empty string at the beginning of a word.
\>      \>       	matches the empty string at the end of a word.
[chars] [chars]	        match any character in the given class; if the
                        first character after [ is ^, match any character
                        not in the given class; a range of characters may
                        be specified by first-last; for example, \W
                        (below) is equivalent to the class [^A\-Za\-z0\-9]
\( \)	( )	        parentheses are used to override operator precedence.
\digit	\digit	        \n matches a repeat of the text matched earlier in
                        the regexp by the subexpression inside the nth 
                        opening parenthesis.
\	\       	any special character may be preceded
                        by a backslash to match it literally.

(the following are for compatibility with GNU Emacs)
\b	\b	        matches the empty string at the edge of a word.
\B	\B	        matches the empty string if not at the edge of a word.
\w	\w	        matches word-constituent characters (letters & digits).
\W	\W	        matches characters that are not word-constituent.

Operator precedence is (highest to lowest) ?, \(*, and +, concatenation,
and finally |.  All other constructs are syntactically identical to
normal characters.  For the truly interested, the file dfa.c describes
(and implements) the exact grammar understood by the parser.

OPTIONS
-A " num"               print <num> lines of context after every matching line
-B " num"               print num lines of context before every matching line
-C                      print 2 lines of context on each side of every match
- num                   print num lines of context on each side of every match
-V                      print the version number on the diagnostic output
-b                      print every match preceded by its byte offset
-c                      print a total count of matching lines only
-e " expr"              search for expr; useful if expr begins with -
-f " file"              search for the expression contained in file
-h                      don't display filenames on matches
-i                      ignore case difference when comparing strings
-l                      list files containing matches only
-n                      print each match preceded by its line number
-s                      run silently producing no output except error messages
-v                      print only lines that contain no matches for the <expr>
-w                      print only lines where the match is a complete word
-x                      print only lines where the match is a whole line

INCOMPATIBILITIES
The following incompatibilities with UNIX grep exist:

  The context-dependent meaning of * is not quite the same (grep only).
  -b prints a byte offset instead of a block offset.
  The {m,n} construct of System V grep is not implemented.

BUGS
  GNU e?grep has been thoroughly debugged and tested over a period
  of several years; we think it's a reliable beast or we wouldn't
  distribute it.  If by some fluke of the universe you discover a bug,
  send a detailed description (including options, regular expressions,
  and a copy of an input file that can reproduce it) to mike@ai.mit.edu.

AUTHORS
  Mike Haertel wrote the deterministic regexp code and the bulk
  of the program.

  James A. Woods is responsible for the hybridized search strategy
  of using Boyer-Moore-Gosper fixed-string search as a filter
  before calling the general regexp matcher.

  Arthur David Olson contributed code that finds fixed strings for
  the aforementioned BMG search for a large class of regexps.

  Richard Stallman wrote the backtracking regexp matcher that is used
  for \digit backreferences, as well as the GNU getopt.  The
  backtracking matcher was originally written for GNU Emacs.

  D. A. Gwyn wrote the C alloca emulation that is provided so
  System V machines can run this program.  (Alloca is used only
  by RMS' backtracking matcher, and then only rarely, so there
  is no loss if your machine doesn't have a "real" alloca.)

  Scott Anderson and Henry Spencer designed the regression tests
  used in the "regress" script.

  Paul Placeway wrote the original version of this manual page.

  Michael Baehr did the port to Windows/NT.