Question

Having heard about Perl for year I decided to give it a few hours of my time to see how much I could pick up. I got through the basics fine and then got to loops. As a test I wanted to see if I could build a script to recurse through all alphanumerical values of up to 4 characters. I had written a PHP code that did the same thing some time ago so I took the same concept and used it. However when I run the script it puts “a” as the first 3 values and then only loops through the last digit. Anyone see what I am doing wrong?

#!/usr/local/bin/perl 

$chars = "abcdefghijklmnopqrstuvwxyz";
$chars .= "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
$chars .= "0123456789";

@charset = split(//, $chars);

$charset_length = scalar(@charset);

sub recurse
{
 ($width, $position, $base_string) = @_;

for ($i = 0; $i < $charset_length; ++$i) {
    $base = $base_string . $charset[$i];
    if ($position < $width - 1) {
        $pos = $position + 1;
        recurse($width, $pos, $base);
    }
    print $base;
    print "\n";
}
}

recurse(4, 0, '');

This is what I get when I run it:

aaaa
aaab
aaac
aaad
aaae
aaaf
aaag
aaah
aaai
aaaj
aaak
aaal
aaam
aaan
aaao
aaap
aaaq
aaar
aaas
aaat
aaau
aaav
aaaw
aaax
aaay
aaaz
aaaA
aaaB
aaaC
aaaD
aaaE
aaaF
aaaG
aaaH
aaaI
aaaJ
aaaK
aaaL
aaaM
aaaN
aaaO
aaaP
aaaQ
aaaR
aaaS
aaaT
aaaU
aaaV
aaaW
aaaX
aaaY
aaaZ
aaa0
aaa1
aaa2
aaa3
aaa4
aaa5
aaa6
aaa7
aaa8
aaa9
aaa9
aaa9
aaa9

Answer 1

You’ve been bitten by non strict scoping, this code does what it should (note the use strict at the top and the subsequent use of my to guarantee variable scoping).

#!/usr/bin/env perl
use strict;
use warnings;

my $chars = "abcdefghijklmnopqrstuvwxyz";
$chars .= "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
$chars .= "0123456789";

my @charset = split(//, $chars);

my $charset_length = scalar(@charset);

sub recurse {
    my ($width, $position, $base_string) = @_;

    for (my $i = 0; $i < $charset_length; ++$i) {
        my $base = $base_string . $charset[$i];

        if ($position < $width - 1) {
            my $pos = $position + 1;
            recurse($width, $pos, $base);
        }

        print $base;
        print "\n";
    }
}

recurse(4, 0, '');