Suidperl

Perl can be run with suid (set user id) permissions using /usr/bin/suidperl.
Automatically enables taint mode.
Script must have suid bit set
/usr/bin/suidperl is suid root, but changes e[ug]id to file's settings.
Be sure to do as little with the increased priviliges!
  open INPUT, "<",  $file1;
  open OUTPUT, ">",  $output;

  # drop privileges asap
  use ENGLISH
  $EGID = $GID;   # set effective to real group id
  $EUID = $UID;   # set effective to real user id

  # use INPUT and OUTPUT as necessary.