use strict;
use warnings;

my $scary_regex = shift;
$scary_regex =~ tr/\cA//d;
# There are now no control-As in the string,
# so I can safely use them as delimiters

my $safe_pat = eval "qq\cA$scary_regex\cA";
my $safe_reg = qr/$safe_pat/;

print "Safe pat is $safe_pat; reg is $safe_reg\n";