View source for Bash =~

=Internal=
* [[Bash_Concepts#.3D.7E|bash Concepts]]

=Overview=

The string to the right of the = ̃ operator is considered an extended regular expression and matched against the string to the left of the operator. The rules governing the extended regular expression are described in regex(3).
<syntaxhighlight lang='bash'>
if [["string_to_be_matched_against_regex" =~ regex ]]; then
  # match 
else
  # no match 
fi
</syntaxhighlight>

Usage is subject to the following constraints:
* The use of &#91;[...]] is required.
* ''DO NOT use double quotes when specifying the regular expression, just specify the regex literal directly.''
* If the regular expression contains spaces, use single quotes to denote space:
<syntaxhighlight lang='bash'>
if [["something" =~ ${regex}' ' ]]; then ...
</syntaxhighlight>
* Variable substitution works for both the string to be matched and the regular expression. When using a variable to specify the regular expression, do not enclose the variable in quotes, use it directly as in the example below:
<syntaxhighlight lang='bash'>
if [[ "${var_containing_string_to_be_matched_against_regex}" =~ ${var_containing_regex} ]]; then ...
</syntaxhighlight>
* It matches &#91;[:space:]]
* If any part of the pattern is quoted, it is forcibly matched as a string.
* The return value is 0 if the string matches the pattern, and 1 otherwise.
* If the regular expression is syntactically incorrect, the conditional expression's return value is 2.
* If the shell option nocasematch is enabled, the match is performed without regard to the case of alphabetic characters.
* The =~ operator has the same precedence as == and !=.

=TODO=

<font color=darkgray>regex(3)</font>