Global search Regular Expression Print
$ grep [OPTION...] PATTERNS [FILE...]
$ grep [OPTION...] -e PATTERNS ... [FILE...]
$ grep [OPTION...] -f PATTERN_FILE ... [FILE...]
grep searches each FILE for PATTERNS. PATTERNS is a string that contains one or more patterns separated by newline characters, and grep prints each line that matches a pattern. When using grep in a shell command, PATTERNS should usually be quoted.
A FILE of "-" denotes standard input. If no FILE is specified, recursive searches examine the working directory, while non-recursive searches read standard input.
Furthermore, the variant programs egrep, fgrep, and rgrep are equivalent to grep -E, grep -F, and grep -r, respectively. These variants are obsolete, but remain available for backward compatibility.
| Character | Description |
|---|---|
| [A-Za-z] | Any lower and upper case letter. |
| [0-9] | Any number. |
| [0-9A-Za-z] | Any lower and upper case letter or digit. |
| Character classes | Description |
|---|---|
| [:alpha:] | Match any alphabetical character, either upper or lower case |
| [:alnum:] | Matches any alphanumeric character 0–9, A–Z, or a–z |
| [[:blank:]] | Matches a space or Tab character |
| [:digit:] | Matches a numerical digit from 0 through 9 |
| [[:lower:]] | Matches any lowercase alphabetical character a–z |
| [[:print:]] | Matches any printable character |
| [[:punct:]] | Matches a punctuation character |
| [[:upper:]] | Matches any uppercase alphabetical character A–Z |
| [[:space:]] | Matches any whitespace character: space, Tab, NL (newline), FF (formfeed), VT (vertical tab), CR (carriage return) |
Unless they are preceded by a backslash, these characters have a special
meaning in BRE.:
^ $ . * [ ] \
However, unless they are preceded by a backslash, these characters have no special meaning.:
? + { } | ( )
Unless they are escaped with a backslash, ERE gives each of these characters a unique meaning:
^ $ . * + ? [ ] ( ) | { }
| Wildcard Character | Description |
|---|---|
| . | Match any Character Except New Line |
| ? | Match 0 or One characters |
| * | Match 0 or More characters |
| + | Match 1 or More characters |
| Quantifier | Description |
|---|---|
| {n} | Matches exactly n times |
| {n,} | Matches n or More |
| {,m} | matches up to m (maximum) |
| {n,m} | Matches between n and m (Minimum, Maximum) |
| ^ | Beginning of line. |
|---|---|
| $ | End of line. |
| ^$ | Empty line. |
| \< | Start of word. |
| \> | End of word. |
| grep ‘alias’ filename | find all occurrences of a string (basic usage)find all occurrences of a string (basic usage) | |
|---|---|---|
| -c | grep -c ‘error’ /var/log/syslog | count the number of matches. |
| -e | grep -e ‘linux$’ filename | use regex (lines ending with 'Linux') |
| -f | grep -f pattern_file .bashrc | take PATTERNS from FILE |
| -i | grep -i ‘Alias’ .bashrc | ignore case search |
| -l | grep -l ‘alias’ /home/traw/* | returns files with matches |
| -L | grep -L ‘alias’ /home/traw/* | returns files without matches |
| -r | grep -r ‘error’ /var/log/log.txt | recursive search (within subdirs) |
| -v | grep -v ‘warning’ /home/traw/log.txt | select non-matching lines |
| -m | grep -m 3 ‘alias’ .bashrc | limit grep Output upto 3 lines. |
| -n | grep -n ‘sudo’ .bashrc | print line numbers of the matches. |
| -o | grep -o ‘search string’ .bashrc | only show the matching part of the string. |
| -x | grep -x ‘linux is love’ filename | match only whole lines |
| -w | grep -w "alias" .bashrc | match only whole words |
| -A | grep -A 6 ‘error’ error.log | print 6 lines after a match |
| -B | grep -B 2 ‘warning’ error.log | print 2 lines before a match |
| -C | grep -C 7 ‘info’ error.log | print 7 lines before and after a match |
| -E | grep -E ‘b(a | e)g’ filename |
Additional anchors and character classes, lookahead/lookbehind, conditional expressions, comments, and other features are available in PCRE.