I recently started working on a CGI program that acted as a gateway between a few Python clients and a large number of XML files on a server. When I started writing the parameter checking code I found myself writing virtually the same code for each subroutine. Having a single separate sub that was flexible enough to check all parameters would keep the code far simpler, shorter, and more maintainable.

What I quickly threw together was a sub that takes a list of acceptable symbols and two numbers indicating whether or not alpha and numeric characters are allowed in the given parameter. It then generates a very simple regex based on the input.

This seems like it would be a fairly common task (there's even a brief mention of it in Programming Perl 3rd ed.) but a quick search here didn't turn up much other than generating regexes? which wasn't quite what I was looking for. Does anyone routinely generate regexes, and if so what types of tasks have you found generating them most useful for. Also, are there any other examples and/or modules available that I should take a look at? Thanks.

Here's the code (any suggestions are greatly appreciated):

use diagnostics;
use strict;
use warnings;

my @randomParameters = ('Abc.123', '../../', 'a@b.c', '789');
my @allowedSymbols   = ('.', '@');
my (@goodParams, @badParams);

checkParam($_, 1, 1, @allowedSymbols) for (@randomParameters);

print $_, " is good\n" for @goodParams;
print $_, " is bad\n"  for @badParams;

sub checkParam {
    my $param   = shift;
    my $alpha   = shift; # if true allow alpha
    my $numeric = shift; # if true allow numeric
    my @symbols = @_;    # allow all symbols in @_

    my $regex = "";

    $regex .= '([a-zA-Z' if $alpha;
    $regex .= '0-9'      if $numeric;

    for my $symbol (@symbols) {
        $regex .= $symbol;
    }
    $regex .= ']*)';

    my $pattern = qr/^${regex}$/;

    if ($param =~ /$pattern/) {
        push(@goodParams, $param);
    } else {
        push(@badParams, $param);
    }


}
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