#!/usr/bin/perl -p

use Getopt::Std;

BEGIN {
	getopts("f:l");
	if ($opt_f) {
		$pre = "^".('[^\t]*\t'x($opt_f-1));
	} else {
		$pre = '';
	}
}

s/($pre)(\d{9}\d*)/$1.convert($2)/geo;

sub convert {
	$s = localtime(shift);
	return $s if $opt_l;
	$s =~ /\d\d:\d\d:\d\d/;
	return $&;
}