Thank you for the clarification. I hope this gets you started.

#!/usr/bin/perl -w
use strict;

my $initial_file   = 'Main';
my $ultimate_level = 2;

sub jak_daxter_recursor_legacy {
    my ($file, $level) = @_;
    
    open (FH, $file) or die "Cannot open $file: $!";
    my $contents = <FH>;
    
    my @filestoprocess = split (/,/, $contents);
    for my $file (@filestoprocess) {
        print "$file\n";
        jak_daxter_recursor_legacy ($file, $level+1)
            unless ($level == $ultimate_level);
    }
}

jak_daxter_recursor_legacy ($initial_file, 1);
[download]

I tested it using three files:
Main, containing 'sub1,sub2'
sub1, containing 'sub12,sub13,sub17'
sub2, containing 'sub21,sub22'

The output is as follows:

sub1
sub12
sub13
sub17
sub2
sub21
sub22
[download]

Hope it helps. If you have any questions, please ask.

Regards,
Luke