I will admit from the start that these may be some of those "dumb a**" questions that some people scowl at, but I'm curious. I was setting up a little demonstration program and I mistyped the following code and got what was a curious output at the time.

First the code (on a HP Netbook running Trisquel/Slaine, Libre-Linux, with Perl 5.10):

#!/usr/bin/perl
#forcount

use strict;
use warnings;

for (my $count = $0; $count < 10; $count++) {
    print "$count\n";
}

[download]

I had not noticed that I had initialised the count with a "$0" instead of "0". I had run "perl -c forcount" and syntax was ok (I regularly forget semicolons). Then, I ran the program and got the following output:


Argument "forcount" isn't numeric in numeric lt (<) at forcount line 5
+.
forcount
1
2
3
4
5
6
7
8
9

[download]

I realised that I had fouled up the initialisation, but was interested to find the filename printed instead of the expected "0".

So, after a bit of investigation, here are my remaining questions:

a) What is the actual purpose of the special scalar variable, $0, which holds the filename of the script (I have read perlvar, but still don't understand the significance);

b) Did I not get a warning about the undeclared variable because it was being assigned to a declared variable, or did I not get it because it was a special variable such as $_ and why should this be the case; and,

c) Did the count iterate to 1..9 because the special scalar variable, $0, was treated as zero due to the numeric lt (<) operator? Or, in other words, how was the condition able to be evaluated if it did not conform to initial expectations by being non-numeric?

I apologise in advance for the "baby Perl" questions.

:There is more than one way to @verb a cat:

In reply to Curious about a quirk with the special variable, $0 by mrdurtal

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