#!/usr/bin/perl
# main program;

use strict;
use warnings;
use Routines;;

{ # closure to avoid global variables
    my $hello = "hello123;

  # ...

    hello( $hello );    

}
__END__

# Routines.pm - a separate file called a "module"

package Routines;
sub hello {
    my $hello = shift;
    print "$hello\n";
}

1;