Hi, I have a variable $format with a regular expression string. Some like "/reg.expr./" (without quotes :-) e.g. /\d+/ for a number. The string is read from a file. How can I check whether this string is a correct reg. expr. (ie. reasonable) or not?

I tried eval() and it look good but I can't find incorrect reg.expr.: 

# $format = "/[12345]/";           #  I expect strings like this
# $format = "/[[12345]//";         #  match "[/"     :-]
# $format = "/aa/[[12345]//";      #  match "aa/[/"

my $success = 1;
my $test = "x";
if ( $format =~ m!^/(.*)/$! ) {    # test for "/reg.expr./" format
    eval { $test =~ m/$1/ };       # test of "user" reg. exp.
    if ( $@ ) {
        $success = 0;              # $format is incorrect reg. expr.
    }
}

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But all my examples look like correct reg. expr.:

Could you find some incorrect reg. expr. for me? Is it possible to use eval() for my check? Thanks.

In reply to How to identify invalid reg. expr.? by armyk

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