Master Linux Regular Expressions: Essential Metacharacters and Practical Examples
This article introduces Linux regular expressions, explains the two types of metacharacters—shell and regex—shows how to enable colored output with grep, provides a sample test file, and demonstrates numerous practical pattern-matching examples ranging from simple word searches to complex character class and repetition constructs.
Regular expressions are character patterns used to match specific strings during a search.
Metacharacters in Linux are divided into two categories:
Shell metacharacters, parsed by the Linux shell.
Regular expression metacharacters, parsed by tools such as vi, grep, sed, awk.
Before the examples, set the grep command with the --color option so matched strings are highlighted.
Create a test file re-file with the following content:
Regular expression metacharacters
Special metacharacters
Extended regular expressions
Practical examples
Match all lines starting with love.
Match all lines ending with love.
Match lines where l starts, any two characters follow, and ends with e.
Match zero or more blank lines followed by love.
Match love or Love.
Match a capital letter A‑Z followed by ove.
Match any character not in the range A‑Z (i.e., all lowercase letters).
Match the literal string love..
Match a space character.
Match any single character.
Match the character o repeated 2 to 4 times.
Match the character o at least twice.
Match the character 0 at most twice.
Match the previous character one or zero times.
Match zero or one character.
Match multiple strings using the alternation operator.
Group filtering and matching.
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