I would do it using File::Basename to separate the path from the filename. This simplifies the task a little: you just have to extract the number from the filename:

#!/usr/bin/perl -w

use strict;
use File::Basename;

while (<>) {
        my ($name, $path, $suffix) = fileparse ($_, ".txt");
        $name =~ /\D+(\d+)/;
        print "number: $1\n";
}
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I hope this helps.

marcos