Why does BASH_REMATCH not work for a quoted regular expression?

Question

The code is like this:

#!/bin/bash
if [[ foobarbletch =~ \'foo(bar)bl(.*)\' ]]
 then
     echo \"The regex matches!\"
     echo $BASH_REMATCH
     echo ${BAS         


        

Answer 1

In your bash REGEX, you should remove quotes. That's why that doesn't work.

If you have space, I recommend to use this way :

#!/bin/bash
x='foo bar bletch'
if [[ $x =~ foo[[:space:]](bar)[[:space:]]bl(.*) ]]
then
    echo The regex matches!
    echo $BASH_REMATCH      
    echo ${BASH_REMATCH[1]} 
    echo ${BASH_REMATCH[2]} 
fi

Answer 2

You can also assign the quoted regexp to a variable:

#!/bin/bash

x='foobarbletch'

foobar_re='foo(bar)bl(.*)'

if [[ $x =~ $foobar_re ]] ; then
    echo The regex matches!
    echo ${BASH_REMATCH[*]}
    echo ${BASH_REMATCH[1]}
    echo ${BASH_REMATCH[2]}
fi

This not only supports simple quoting but gives the regexp a name which can help readability.

Answer 3

Thanks to your debugging statement, echo The regex matches!, you should have noticed there is no problem with BASH_REMATCH, since the if statement evaluates to false.

In bash, regular expressions used with =~ are unquoted. If the string on the right is quoted, then it is treated as a string literal.

If you want to include whitespaces in your regex's, then use the appropriate character classes, or escape your space if you want a space.