'g'=~/g/;
my $regex = 'm{}g';  # user input
my $text = 'x';      # user input
eval qq{
	use re 'debug';
	print "<\$&>\\n" while \$text =~ $regex;
};

##</code><code>##

Compiling REx ""
Final program:
   1: NOTHING (2)
   2: END (0)
minlen 0 
Freeing REx: ""