grep(1)
NAME
grep, egrep, fgrep − search a file for a pattern
SYNTAX
grep [ option... ] expression [ file... ]
egrep [ option... ] [ expression ] [ file... ]
fgrep [ option... ] [ strings ] [ file ]
DESCRIPTION
Commands of the grep family search each input file (standard input default) for lines matching a limited regular expression. 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.
The grep limited regular expressions are in the style of ed(1). It uses a compact nondeterministic algorithm. The egrep patterns are full regular expressions. It uses a fast deterministic algorithm that sometimes needs exponential space. The fgrep patterns are fixed strings, and, thus it is fast and compact.
OPTIONS
−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 − (dash).
−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 ´ ´.
The fgrep command searches for lines that contain one of the (newline-separated) strings.
The egrep command 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.
RESTRICTIONS
Ideally there should be only one grep, but we do not know a single algorithm that spans a wide enough range of space-time tradeoffs.
Lines are limited to 256 characters; longer lines are truncated.
DIAGNOSTICS
Exit status is 0 if any matches are found, 1 if none, 2 for syntax errors or inaccessible files.