#!/usr/bin/perl -w

use strict;

my	@TestData =
(
	'NT8',
	'NT9',
	'NT10',
	'NT11',
);


{
	foreach my $inputData (@TestData)
	{
		my $outputData = $inputData;
		while (length($outputData) < 4)
		{
			$outputData .= '_';
		}
		printf "%-4s -> %s\n", $inputData, $outputData;
	}
}

exit;

__END__


C:\Steve\Dev\PerlMonks\P-2013-09-17@2038-Use-Strict>make4len.pl
NT8  -> NT8_
NT9  -> NT9_
NT10 -> NT10
NT11 -> NT11