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; unless the −h flag is used, the file name is shown if there is more than one input file. 

Grep patterns are limited regular expressions in the style of ed(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. 

−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 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. 

−s No output is produced, only status. 

−h Do not print filename headers with output lines. 

−y Lower case letters in the pattern will also match upper case letters in the input (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. 

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

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 matches that character. 

The character ^ ($) matches the beginning (end) of a line. 

A .  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 * (+, ?) matches a sequence of 0 or more (1 or more, 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.

SEE ALSO

ed(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

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. 

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

7th Edition