#!/bin/sh

eval "exec /usr/software/bin/perl5.8.0 -I`pwd` -Mcheckem -e main $*"
    if $running_under_some_shell;

package main;

sub main {
    print "Hello from main\n";
    <useful code here>
}

##</code><code>##

#!/bin/sh

DIR=`dirname $0`
BASE=`basename $0 | sed -e 's/\.pm\$//'`
eval "exec /usr/software/bin/perl5.8.0 -I$DIR -M$BASE -e main $*"
    if $running_under_some_shell;

package main;
...