this works (assuming you want a series of numbers but disregarding leading zeros):

use strict;

my $file = 'file013.txt';
my ($sk) = $file =~ m/0*(\d+)/;

print $sk;
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The problem with the way you had it is that it is returning 1 not because of the number 1 in the 013 but because it is true (akai.e., there was a match).

-enlil