How to use Regular expression (regex) in Bash?

About

This article shous you how to use regular expression in Bash

Example

Conditional

tomatch='/php-status?full&json'
[[ "$tomatch" =~ '/php-status' ]] && echo match || echo does not match
[[ ! "$tomatch" =~ 'not' ]] && echo does not match || echo does match

Group Capture

This example shows you how you can capture a Group to extract text.

Example where we will extract a part of a file name

fileName="helloWorld.jpg"

# The regular expression starts with $' and ends with '
regex=$'(.*)\.jpg'

# double bracket is mandatory to use the regular expression operators
if [[ $fileName =~ $regex ]]
then
	name="${BASH_REMATCH[1]}"
	echo ${name}
else
	echo "$fileName doesn't match" 
fi

How it works? With the Bash Binary operator

When the regexp binary operator =~ is used, the string to the right of the operator is considered an extended regular expression and matched accordingly.

The operator has the same precedence as == and !=

The return value is:

• 0 if the string matches the pattern
• 2 if the regular expression is syntactically incorrect
• 1 otherwise.

Others:

• If the shell option nocasematch is enabled, the match is performed without regard to the case of alphabetic characters.
• Any part of the pattern may be quoted to force it to be matched as a string.
• Capturing group are saved in the BASH_REMATCH variable.

Glob

Note that pathname expansion use globbing as well as the control flow structure such as case

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