$ cat t.pl
use strict;
use warnings;

my $re1 = qr/p/;
my $re2 = qr/t/;

use re qw(Debug More);

my @list = ('alpha', 'beta', 'gamma', 'delta');

for (@list) {
    print $_, "\n";
    if (/$re1/) { print "has P\n" }
    if (/$re2/) { print "has T\n" }
}

$ perl -d t.pl
   <<< snip >>>
main::(t.pl:4):	my $re1 = qr/p/;
  DB<1> s
main::(t.pl:5):	my $re2 = qr/t/;
  DB<1> 
main::(t.pl:9):	my @list = ('alpha', 'beta', 'gamma', 'delta');
  DB<1> 
main::(t.pl:11):	for (@list) {
  DB<1> 
main::(t.pl:12):	    print $_, "\n";
  DB<1> 
alpha
main::(t.pl:13):	    if (/$re1/) { print "has P\n" }
  DB<1> 
main::(t.pl:13):	    if (/$re1/) { print "has P\n" }
  DB<1> 
has P
main::(t.pl:14):	    if (/$re2/) { print "has T\n" }
  DB<1> p { use re qw(Debug More); $re1=qr/g/; }
Compiling REx "g"
Final program:
   1: EXACT <g> (3)
   3: END (0)
anchored "g" at 0 (checking anchored isall) minlen 1 
  DB<2> s
main::(t.pl:12):	    print $_, "\n";
  DB<2> 
beta
main::(t.pl:13):	    if (/$re1/) { print "has P\n" }
  DB<2> 
Guessing start of match in sv for REx "g" against "beta"
Did not find anchored substr "g"...
Match rejected by optimizer
main::(t.pl:14):	    if (/$re2/) { print "has T\n" }
  DB<2> 
main::(t.pl:14):	    if (/$re2/) { print "has T\n" }
  DB<2> 
has T
main::(t.pl:12):	    print $_, "\n";
  DB<2>