I'd do (untested): 
my $re = input-from-user;
eval {my $dummy = qr/$re/; 1} or die "Illegal regexp";

[download]
You might want to use use re "eval" if you want your users to use (?{ }) and (??{ }). Of course, you only do that if you can trust your users.

In reply to Re: Input Validation - verifying a string is a properly formatted regular expression by JavaFan
in thread Input Validation - verifying a string is a properly formatted regular expression by morpheous1129

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