#!/usr/bin/perl

my $Usage = "$0  input_file.name  output_file.name\n";
( @ARGV == 2 and -f $ARGV[0] ) or die $Usage;

open( IN, "<", $ARGV[0] ) or die "$ARGV[0]: $!";
open( OUT, ">", $ARGV[1] ) or die "$ARGV[1]: $!";

while (<IN>) {
    tr/a-zA-Z/A-Za-z/;  # invert case, just for fun
    print OUT;
}