NAME
grep, egrep, fgrep - search a file for a pattern

SYNOPSIS
grep [ option ] ... expression [ file ] ...

egrep [ option ] ... [ expression ] [ file ] ...

fgrep [ option ] ... [ strings ] [ file ]

DESCRIPTION
Commands of the grep family search the input files (standard input
default) for lines matching a pattern. Normally, each line found
is copied to the standard output. Grep patterns are limited
regular expressions in the style of ex(1); it uses a compact
nondeterministic algorithm. Egrep patterns are full regular
expressions; it uses a fast deterministic algorithm that sometimes
needs exponential space. Fgrep patterns are fixed strings; it is
fast and compact. The following options are recognized.

-v All lines but those matching are printed.

-x (Exact) only lines matched in their entirety are printed
(fgrep only).

-c Only a count of matching lines is printed.

-l The names of files with matching lines are listed (once)
separated by newlines.

-n Each line is preceded by its relative line number in the file.

-b Each line is preceded by the block number on which it was
found. This is sometimes useful in locating disk block
numbers by context.

-h Never print filename headers with output lines.

-o Always print filename headers with output lines.

-i The case of letters is ignored in making comparisons - that
is, upper and lower case are considered identical.

-s Silent mode. Nothing is printed (except error messages).
This is useful for checking the error status.

-w The expression is searched for as a word (as if surrounded by
‘<’ and ‘>’, see ex(1).) (grep only)

-e expression
Same as a simple expression argument, but useful when the
expression begins with a -.

-f file
The regular expression (egrep) or string list (fgrep) is taken
from the file.

In all cases the file name is shown if there is more than one input
file. Care should be taken when using the characters $ * [ ^ | ( )
and  in the expression as they are also meaningful to the Shell.
It is safest to enclose the entire expression argument in single
quotes ’ ’.

Fgrep searches for lines that contain one of the (newline-
separated) strings.

Egrep accepts extended regular expressions. In the following
description ‘character’ excludes newline:

A  followed by a single character other than newline matches
that character.

The character ^ matches the beginning of a line.

The character $ matches the end of a line.

A . (period) matches any character.

A single character not otherwise endowed with special meaning
matches that character.

A string enclosed in brackets [] matches any single character
from the string. Ranges of ASCII character codes may be
abbreviated as in ‘a-z0-9’. A ] may occur only as the first
character of the string. A literal - must be placed where it
can’t be mistaken as a range indicator.

A regular expression followed by an * (asterisk) matches a
sequence of 0 or more matches of the regular expression. A
regular expression followed by a + (plus) matches a sequence
of 1 or more matches of the regular expression. A regular
expression followed by a ? (question mark) matches a sequence
of 0 or 1 matches of the regular expression.

Two regular expressions concatenated match a match of the
first followed by a match of the second.

Two regular expressions separated by | or newline match either
a match for the first or a match for the second.

A regular expression enclosed in parentheses matches a match
for the regular expression.

The order of precedence of operators at the same parenthesis level
is [] then *+? then concatenation then | and newline.

Ideally there should be only one grep, but we don’t know a single
algorithm that spans a wide enough range of space-time tradeoffs.

SEE ALSO
ex(1), sed(1), sh(1)

DIAGNOSTICS
Exit status is 0 if any matches are found, 1 if none, 2 for syntax
errors or inaccessible files.

BUGS
Lines are limited to 256 characters; longer lines are truncated.