Perhaps this snippet can be made to do what you want.

use strict;
use warnings;

my $string = "This is a test.";
my $re = "s/test/TEST/i";
eval "if( \$string =~ $re ) { print qq/Yep\n/; }";
warn $@ if $@;
print $string, "\n";
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qr// allows you to pass the meat of a regular expression around compiled within a scalar variable. qr// doesn't allow for the regexp quotish operators to be embedded within (as in qr[s///].... that doesn't work), because it is not intended to contain any kind of code except for the meat of a regexp. If you want to pass a piece of actual code around as though it were a string, the way to execute the string is to eval it.

As Aristotle pointed out, you always have to think carefully when you pass quotes or quote-like operators within a quoted string. But if you ask how to do a tricky thing, you get a tricky solution. ;) eval is never for the faint of heart. As Aristotle points out, it's safer and cleaner to pass a code ref rather than stringified code.