How to drop privileges in a Perl script when initially run as root

drop_privileges.pl

BEGIN { # give up root identity and run as an unprivileged user ASAP

   use POSIX;
  
   my $run_as = 'user_you_want_to_run_as';

   my ( $uid, $gid ) = ( getpwnam $run_as )[ 2, 3 ];

   die $! unless $uid && $gid;

   if ( $> == 0 )
   {
      POSIX::setgid( $gid ); # GID must be set before UID!
      POSIX::setuid( $uid );
   }
   elsif ( $> != $uid )
   {
      warn <<__ABORT__ and exit 1;
** ABORT! **
   This application only runs as the "$run_as" user,
   not as your user account with ID: $>
__ABORT__
   }
}