Bash =~

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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).

if [[ "string_to_be_matched_against_regex" =~ regex ]]; then
  # match 
  # no match 

Usage is subject to the following constraints:

  • The use of [[...]] is required.
  • ⚠️DO NOT use double quotes when specifying the regular expression, just specify the regex literal directly. If you do double quote the right-hand side string, =~ will still work but it will match the quoted string literally rather than a regular expression.
  • Variable expansion is performed, the following expression is valid:
if [["something" =~ ${regex} ]]; then ...
  • If the regular expression contains spaces, use single quotes to denote space:
if [["something" =~ ${regex}' ' ]]; then ...

This also works:

[[ "${output}" =~ "chart type".*"required" ]]
  • Variable substitution works for both the string to be matched and the regular expression. When using a variable to specify the regular expression, do not enclose the variable in quotes, use it directly as in the example below:
if [[ "${var_containing_string_to_be_matched_against_regex}" =~ ${var_containing_regex} ]]; then ...
  • It matches [[: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 !=.


See man re_format.

Single digits:


Multiple digits:



A string that does not contain a slash:

if [[ ${something} =~ ^[^/]*$ ]]; then

Multiple spaces at the end:

if [[ ${something} =~ ^blah' '*$ ]]; then