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.