Use of uninitialized value in string eq. left or right?

I am clearing up some code and I see in our server logs that the perl error is ...

Use of uninitialized val开发者_开发问答ue in string eq at .....

Looking at the code the line looks like this....

if ($level1 eq $level2) {

OK fair enough. I suppose my question is this. Is it $level1 or $level2 that's the problem?

I wrote a quick test to try to replicate it locally and it looks like this....

#!/usr/bin/perl
use warnings;
my $a;
my $b;

if ($a eq $b){
    print "....";
}

And I get a much more informative error.

Use of uninitialized value $a in string eq at ./warntest.cgi line 7.
Use of uninitialized value $b in string eq at ./warntest.cgi line 7.

This is seemingly inconsistent behavior. Does anyone have a clue? Janie

The indication of which variable was undef was added to the warning (where easily possible) in perl 5.10 (to much cheering). Your server is likely using an older perl.