what is =~ in following script

Question

this script check that a directory is a parent of another. how to work this script?

     T() {
          if [[ "$2" =~ ${1}['/'?] ]] ; then
              echo "$2 is child of $1"
              return 0
          else
              echo "$2 is NOT child of $1 ($?)"
              return 1
          fi
         }

Read the [`bash` manual page](http://linux.die.net/man/1/bash). — Some programmer dude, Aug 07 '13 at 07:52
Your question is phrased ambiguously. Do you want to know how this script is working - in particular what the `~=` is doing, or how to use this script? Please clarify it. — Chen Levy, Aug 07 '13 at 08:06
To avoid confusion about what's going on here, [we took the liberty to do some experiments with this questions](http://meta.stackexchange.com/questions/192242/you-made-too-few-changes-to-the-post-to-improve-it). — Bobby, Aug 07 '13 at 08:13

score 2 · Answer 1 · answered Aug 07 '13 at 07:52

2

It's a regular expression match, a helpful tool to match a string to a pattern. This link may help you.

answered Aug 07 '13 at 07:52

Miguel Prz

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score 2 · Answer 2 · answered Aug 07 '13 at 07:52

2

It is a regular expression pattern match operator. See the bash reference manual under Conditional constructs — and look for the [[ ... ]] construct.

answered Aug 07 '13 at 07:52

Jonathan Leffler

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score 1 · Accepted Answer · answered Aug 07 '13 at 07:54

From manual:

An additional binary operator, ‘=~’, is available, with the same precedence as ‘==’ and ‘!=’. When 
it is used, the string to the right of the operator is considered an extended regular expression 
and matched accordingly (as in regex3)). The return value is 0 if the string matches the pattern, 
and 1 otherwise.

what is =~ in following script

3 Answers3