GREP

Section: User Commands (1)
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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.


 

Index

NAME
SYNOPSIS
DESCRIPTION
SEE ALSO
DIAGNOSTICS
BUGS

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Time: 10:16:13 GMT, December 28, 2024