Something that will help you is to use strictures (use strict; use warnings;). They pick up errors and questionable code early.

In the case of Perl being shown a non-integer string in a context where a number is expected use warnings; would tell you that something odd is happening:

use strict;
use warnings;

my $notAnInt = '#10';

print "It's 10\n" if $notAnInt == 10;
print "It's 0\n" if $notAnInt == 0;
print "It's #10\n" if $notAnInt eq '#10';
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prints:

Argument "#10" isn't numeric in numeric eq (==) at noname1.pl line 6.
It's 0
It's #10
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Note that a non-numeric string tends to be numified as 0.