# replacing system("date") with:
defined(my $pid = fork) or die "Cannot fork: $!";
unless($pid) { # I'm the child
  # make your env changes here
  # you can also change directory, umask, priority, etc.
  exec "date";
  die "date not found (just like me last friday night)";
}
# parent continues here...
{
  # to emulate system(), we need to ignore INT and QUIT
  # while the kid is foreground
  local $SIG{INT} = local $SIG{QUIT} = 'IGNORE';
  waitpid($pid, 0);
}