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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.

MetacharacterDescription
.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.
\bMatches empty string at the edge of a word.
\BMatches 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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