use warnings;

$main::look{mom} = "works";
my $var = "It works!";
if ( $var =~ /$main::look{mom}/ ) {
    print "Guess what!  It matched!\n";
}

##</code><code>##

use strict;
use warnings;

my $test_interpolation = "Old McDonald had a farm?.";

if ( "Old McDonald had a fart " =~ m/$test_interpolation/ ) {
    print "Ewwwww!\n";
}
__OUTPUT__
Ewwwww!