Seems like you could eval it safely without compromising too much functionality if you chose some unlikely delimiters and eliminated them from the input: 
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";

[download]
Is there danger here that I don't see?

Update: Pustular Postulant pointed out that you could go straight to the regex, rather than having the intermediate $safe_pat string (just use qr instead of qq). When I was putting it together, something told me that wasn't safe, but I think it is.
Also note that \cA on the input works fine, if you actually want control-A in your pattern.

Caution: Contents may have been coded under pressure.

In reply to Re: qr/string/ is not the same as qr/$var/ ? by Roy Johnson
in thread qr/string/ is not the same as qr/$var/ ? by grinder

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