Bash - Regex

About

Multilingual Regular Expression Syntax (Pattern) in Bash

Example

Conditional

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

Group Capture

Group capture

f="helloNico.jpg"
regex=$'[0-9]+_([a-z]+)_[0-9a-z]*'

# double bracket is mandatory
if [[ $f =~ $regex ]]
then
	name="${BASH_REMATCH[1]}"
	echo "${name}.jpg"    # concatenate strings
	name="${name}.jpg"    # same thing stored in a variable
else
	echo "$f doesn't match" >&2 # this could get noisy if there are a lot of non-matching files
fi

Bash Binary operator

When the additional 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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