use warnings;
use strict;

if (@ARGV != 3){
    print "Program requires 3 arguments\n";
    exit;
}

my ($one, $two, $three) = @ARGV;

print "arg1: $one, arg2: $two, arg3: $three\n";

##</code><code>##

> perl def.pl
Program requires 3 arguments

> perl def.pl 1 2 3
arg1: 1, arg2: 2, arg3: 3