Eh?
I'm going to make an assumption (dangerous, I know), and assume you're talking about this behaviour:

#!/usr/bin/perl

use warnings;
use strict;
use diagnostics;

my $foo = 1;

if($foo = 2) {
        print "Boo!\n";
}
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... which produces the output:

Found = in conditional, should be == at hole.pl line 8. (#1)
    (W syntax) You said
    
        if ($foo = 123)
    
    when you meant
    
        if ($foo == 123)
    
    (or something like that).

Boo!
[download]

... which kind of explains it really.