What fun!

#!/usr/bin/perl
use warnings;
use strict;
$\ = "\n";

$_ = "123123123";
my %x = ( 9 => "abc", foo => "abc" );

eval '/^$x{9}$/';
print '1.  "$x" requires explicit package name' if $@;

my $x = "[123]";

print "2.  matches"  if /^$x{9}$/;
print "3.  matches"  if /^$x{5,12}$/;

my $nine = 9;

print "4.  no match" unless /^$x{foo}$/;
print "5.  no match" unless /^$x{"9"}$/;
print "6.  no match" unless /^$x{0+9}$/;
print "7.  no match" unless /^$x{$nine}$/;

print "8.  matches"  if /^${x}{$nine}$/;
print "9.  matches"  if /^${x}{9}$/;
print "10. no match" unless /^${x}{0+9}$/;
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