#!/usr/bin/perl -w

use strict;
# Error checking!
die "Required argument missing!\n" unless ($#ARGV > 0);

# This along with the following code ensures a positive numeric range.
my $last = 0;

# More Error handling!
for (@ARGV) {
    # Ensures numeric input!
    die "Argument \"$_\" is not numeric!\n" unless (/\d+/);
    # Ensures a negative number was not entered as first argument and
    # also that the second argument is higher in value then the first.
    die "Invalid range!\n" unless ($_ > $last);
    $last = $_;
}

# Here we know that there was some sort of input at command line.
# We also know that each argument is numeric.
# We also know that the user gave a valid range in order for the app
# to print out a consecutively increasing numeric count.
# So with all the error handling passed if the program gets to this point.
# we know we have the required VALID command line input in order for us to
# successfully run this program.
for ($ARGV[0] .. $ARGV[1]) { print; print"\n"; }