use Perl

Yesterday my friend Allan mailed me a script, he could not understand did not work for me to have a look at.

After debugging using the Perl debugger, trying all kind of tricks and reading some documentation, I started to suspect a bug in Perl, when I later talked to him, he had made an even smaller version of the and he mailed it to me.

I ended up writing my own barebones version of the demo, which demonstrates the problem:

use strict;
 
my $str = q(
J:somestring
I:someother
);
 
my $i = 0;
my $err = "\t### ERR ###\n\tNo match\n";
my $success = "\tsuccess...\n";
 
foreach my $key ("J","I") {
    my $str2 = $str;
 
    print "### RUN 1/".++$i." ###\nTesting \$str ... looking for $key\n";
    if ($str =~ m/^$key:.+/gm) {
        print "$success\n";
    } else {
        print "$err\n";
    }
 
    print "Testing \$str2 ... looking for $key\n";
    if ($str2 =~ m/^$key:.+/gm) {
        print "$success\n";
    } else {
        print "$err\n";
    }
}
 
foreach my $key ("I","J") {
    my $str2 = $str;
 
    print "### RUN 2/".++$i." ###\nTesting \$str ... looking for $key\n";
    if ($str =~ m/^$key:.+/gm) {
        print "$success\n";
    } else {
        print "$err\n";
    }
 
    print "Testing \$str2 ... looking for $key\n";
    if ($str2 =~ m/^$key:.+/gm) {
        print "$success\n";
    } else {
        print "$err\n";
    }
}

The problem see to be the /g operator in the regular expressions when it is removed the thing works and as the demo shows, when 'J' comes before 'I' there is no problem.

This is the output:

### RUN 1/1 ###
Testing $str ... looking for J
        success...
 
Testing $str2 ... looking for J
        success...
 
### RUN 1/2 ###
Testing $str ... looking for I
        success...
 
Testing $str2 ... looking for I
        success...
 
### RUN 2/3 ###
Testing $str ... looking for I
        ### ERR ###
        No match
 
Testing $str2 ... looking for I
        success...
 
### RUN 2/4 ###
Testing $str ... looking for J
        success...
 
Testing $str2 ... looking for J
        success...

If you alter the string so the part containing 'I' comes before the part that contains 'J', the problem is with 'J'.

I have searched for the string 'regex' at rt.perl.org only to be presented with 72 tickets. I have looking through some of these, but I have not yet found out whether this bug is already known.