G'day almsdealer,

Welcome to the Monastery.

Given you're very new to Perl, you've made a great start! Though you're problem has already been solved (by the redoubtable haukex) I'd like to offer a couple of tips to help you on your Perl journey:

• Always use parens when calling user-defined subroutines (see here for why).
• Use Perl's core B::Deparse module to see how Perl parses your script.

For example, with your script saved as almsdealer.pl, running:

perl -MO=Deparse,-p almsdealer.pl >deparse.pl
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allows you to see how Perl parses your script, in your case deparse.pl contains:

use strict;
use warnings;
sub myTrim {
    (my($str) = @_);
    (my($trimmed) = ($str =~ /\s*(.*)\s*/));
    (return $trimmed);
}
(my(@allTags) = ());
foreach my $file (glob('[0-9][0-9][0-9][0-9].txt')) {
    use File::Glob ();
    (my(@fileTags) = ());
    (open(my $handle, '<', $file) or die(q[couldn't open file]));
    while (defined((my $line = readline($handle)))) {
        do {
            if (($line =~ /^tags/)) {
                (my($tagsString) = ($line =~ /^tags\s+(.*)/));
                (@fileTags = (@fileTags, split(/,/, $tagsString, 0)));
            }
        };
    }
    close($handle);
    (my(%uniqueTags) = map({myTrim($_, 1);} @fileTags));
    (@allTags = (@allTags, keys(%uniqueTags)));
}
print(("@allTags\n"));
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Hopefully, seeing myTrim($_, 1) will set alarm bells ringing because your myTrim function takes one argument, not two.

As a matter of personal style, I would write your:

    my ($str) = @_;
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as:

    my $str = shift;    # the string to be trimmed
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because I like to put a comment next to each parameter describing what it does, plus this style scales nicely for subroutines that take more than one argument (a random example of this style can be found here).

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