bash 3.2 regex pattern not matched while using =~

Question

I'm trying to match a simple regex in a bash script. It behaves as expected with GNU bash, version 4.2.24(1)-release (x86_64-pc-linux-gnu) but does not with GNU bash, version 3.2.25(1)-release (x86_64-redhat-linux-gnu)

here is the code:


#!/bin/bash

line="[foo]"
[[ $line =~ ^\[.*\]$ ]] && echo "regex matched"
echo "value of \$? : " $?
echo "value of BASH_REMATCH : " $BASH_REMATCH
/bin/bash --version|grep "GNU bash"

here is the output with GNU bash, version 4.2.24(1)-release (x86_64-pc-linux-gnu)

regex matched
value of $? : 0
value of BASH_REMATCH : [foo]
GNU bash, version 4.2.24(1)-release (x86_64-pc-linux-gnu)

here is the output with GNU bash, version 3.2.25(1)-release (x86_64-redhat-linux-gnu)

value of $? : 1
value of BASH_REMATCH :
GNU bash, version 3.2.25(1)-release (x86_64-redhat-linux-gnu)

I've read a lot of post here and elsewhere regarding the behaviors of the oparator in =~ and I can't find anyone who haves the same problem. I saw that there were major changes in bash 3.2 but as far as I see it should work from 3.2 onward.

Please take note that I've already tried to include it in a case statement, as in: "case $line in ^\[.*\]$ )" — vinni_f
– vinni_f, Commented Mar 6, 2013 at 17:17

Mat · Accepted Answer · 2013-03-06 17:23:34Z

2

Looks like some form of escaping problem.

This works here (bash version 3.2.25(1)-release):

line="[foo]"
bar="^\[.*\]$"
[[ $line =~ $bar ]] && echo "regex matched"

This also appears to work:

[[ $line =~ ^\\[.*\\]$ ]] && echo "regex matched"

answered Mar 6, 2013 at 17:23

Mat

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3 Comments

vinni_f Over a year ago

All right @Mat. Your first solution is working on both versions. I must say that I tried doing: [[ $line =~ "^\[.*\]$" ]] before posting but it was not behaving as expected. Doing bar="^\[.*\]$" then [[ $line =~ $bar ]] works. Do you know what's the difference between these 2 ways of wrinting?

vinni_f Over a year ago

Your second solution does not work in GNU bash, version 4.2.24(1). Merci ;)

Mat Over a year ago

I don't really know why what you had didn't work, or, for that matter, why the double-escaped one does (in 3.2). Might be a bug. See this bash FAQ item E14 for some info related to bash versions and that [[ =~ ]] thing. The "stuff it in a variable" trick works well enough.

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