Linux Regular Expression Regular expression is also called regex or regexp. It is a very powerful tool in Linux. Regular expression is a pattern for a matching string that follows some pattern. Regex can be used in a variety of programs like grep, sed, vi, bash, rename and many more.
Regular Expression Metacharacters A regular expression may have one or several repeating metacharacters.
Metacharacter |
Description |
. |
Replaces any character. |
^ |
Matches start of string and represents characters not in the string. |
$ |
Matches end of string. |
* |
Matches zero or more times the preceding character. |
\ |
Represents the group of characters. |
() |
Groups regular expressions. |
? |
Matches exactly one character. |
+ |
Matches one or more times the preceding character. |
{N} |
Preceding character is matched exactly N times. |
{N,} |
Preceding character is matched exactly N times or more. |
{N,M} |
Preceding character is matched exactly N times, but not more than N times. |
- |
Represents the range. |
\b |
Matches empty string at the edge of a word. |
\B |
Matches empty string if it is not at the edge of a word. |
\< |
Matches empty string at the beginning of a word. |
\> |
Matches empty string at the end of a word. |
Regex Versions There are three versions of regular expressions syntax:
- BRE : Basic Regular Expressions
- ERE : Extended Regular Expressions
- PRCE: Perl Regular Expressions
Depending on tool or programs, one or more of these versions can be used.
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