Question

DON’T ASK WHY but…

I have a regex that needs to be case insensitive if run on windows BUT case sensitive when run on *nix.

Here is an example snippet of what I am kind-of doing at the moment.

sub relative_path 
{
    my ($root, $path) = @_;

    if ($os eq "windows")
    {
        # case insensitive with regex option 'i'
        if ($path !~ /^\Q$root\E[\\\/](.*)$/i)
        {
            print "\tFAIL:$root not in $path\n";
        }
        else
        {
            return $1;
        }
    }
    else
    {
        # case sensitive
        if ($path !~ /^\Q$root\E[\\\/](.*)$/)
        {
            print "\tFAIL:$root not in $path\n";
        }
        else
        {
            return $1;
        }
    }
    return "";
}

Argh! The repetition hurts my OCD but my perl-fu is weak. Somehow I want to make the regex option ‘i’ for case-insensitive conditional but I don’t now how?

Answer 1

You can create patterns and store them in scalars using the qr operator:

sub relative_path 
{
    my ($root, $path) = @_;

    my $pattern = ($os eq "windows") ? qr/^\Q$root\E[\\\/](.*)$/i : qr/^\Q$root\E[\\\/](.*)$/;

    if ($path !~ $pattern)
    {
        print "\tFAIL:$root not in $path\n";
    }
    else
    {
        return $1;
    }
}

This might not be 100% perfect, but hopefully you should get the idea.

Make sure to check out the section “Quote and Quote-Like Operators” in perlop.

---

EDIT: Okay, here’s a DRY solution since people are complaining about it.

sub relative_path 
{
    my ($root, $path) = @_;

    my $base_pattern = qr/^\Q$root\E[\\\/](.*)$/;
    my $pattern = ($os eq "windows") ? qr/$base_pattern/i : $base_pattern;

    if ($path !~ $pattern)
    {
        print "\tFAIL:$root not in $path\n";
    }
    else
    {
        return $1;
    }
}