Passing a regex substitution as a variable in Perl?

Question

I need to pass a regex substitution as a variable:

sub proc {
    my $pattern = shift;
    my $txt = \"foo baz\";

    $txt =~ $pattern;
}

my $pattern = \'s         


        

Answer 1

s/// is not a regex. Thus, you can't pass it as a regex.

I don't like eval for this, it's very fragile, with a lot of bordercases.

I think it's best to take an approach similar to the one Javascript takes: pass both a regex (in Perl, that is qr//) and a code reference for the substitution. For example, to pass parameters to get the same effect as

s/(\w+)/\u\L$1/g;

You can call

replace($string, qr/(\w+)/, sub { "\u\L$1" }, 'g');

Note that the 'g' modifier is not actually a flag for the regex (I think attaching it to the regex is a design mistake in Javascript), so I chose to pass it in a 3rd parameter.

Once the API has been decided on, implementation can be done next:

sub replace {
    my($string, $find, $replace, $global) = @_;
    unless($global) {
        $string =~ s($find){ $replace->() }e;
    } else {
        $string =~ s($find){ $replace->() }ge;
    }
    return $string;
}

Let's try it:

print replace('content-TYPE', qr/(\w+)/, sub { "\u\L$1" }, 'g');

Result:

Content-Type

That looks good to me.