$SIG{CHLD} = 'IGNORE'; # ignore dead children, to avoid zombie processes

my $child = fork();

if ($child) { # parent; return data
  $self->return_data( { data => $data } );
} else { # child; run external process

  my $child_output;
  eval { # gather a whole lot of data; assemble $external_command
    use IPC::System::Simple 'capture';
    $child_output = capture($external_command);
  };

  $self->log("Error when running [$external_command]: $child_output") if $child_output;
  $self->log("Error when running [$external_command]: $@") if $@;

  CORE::exit(0);
}

##</code><code>##

Error when running [{external command}]: "{external command}" failed to start: "No child processes" at /path/to/web/program.pm line 459.