#!/usr/bin/perl

($dir) = @ARGV;
open (MYFILE, '>>data.txt') || die;
&loopDir($dir, "");
exit;

sub loopDir {
    $dir = "." unless $dir;
    local($dir, $margin) = @_;
    chdir($dir) || die "Cannot chdir to $dir\n";
    local(*DIR);
    opendir(DIR, ".");
    while ($f=readdir(DIR)) {
        next if ($f eq "." || $f eq "..");
        print MYFILE "$margin$f\n";
        if (-d $f) {
            &loopDir($f,$margin."   ");
        }
    }
    closedir(DIR);
    chdir("..");
}
close (MYFILE);
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im trying to avoid using cpan for this project

Bad idea. Your code is also sub-optimal:

• use strict missing
• & in front of function calls does not do what you think. Get rid of it, this ain't ancient Perl 4.
• local instead of my
• Recursion in loopDir will eventually run out of handles. Collect all subdirectories, then recurse after closing the directory handle. Or use a directory queue (shift the directory to read from, push every new directory found, run until queue is empty) and completely get rid of the recursion.
• close (MYFILE) is unreachable due to exit in front of it
• Two-argument open instead of three-argument open. Do you really need to support perl < 5.6 (more than twelve years old)?
• Bareword file handles instead of lexical ones
• open || die instead of open or die, same problem with chdir
• die without an error message ($!)
• opendir lacks an error check.

Alexander

--
Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)