Simple package for ensuring that a script is run as a given user

run-as.pl

#!/usr/bin/perl

package Must::Run::As;

sub import {
        my ($package,$user) = @_;
        unless( $user ){
                $user = 'mail';
        }
        die "Must run as $user\n" unless ( getpwuid( $< ) eq $user );
}

package MAIN;

import Must::Run::As 'foobs';

print "Running as " . getpwuid( $< ) . "\n";