As BUU mentioned, the use of qw seems a little, strange, but it works anyway, it deparses to:
$cwd =~ m[(/.*)/];
But if you don't use it for the sake of obfuscation, I suggest to replace it by something more readable. :)

My guess why your code doesn't work is either dirname $0 or $0 is not what you expect. Add some print statements for debugging to see what they contain.
Also, you should check if the regex matches, $1 will only be set if the match is successful:

if ( $cwd =~ m#(/.*)/# ) {
    $cwd = $1;
    print $cwd;
}
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