++ed by:
4 non-PAUSE users
Author image Michael Conrad
and 4 contributors


Proc::Background::Win32 - Windows-specific implementation of process create/wait/kill


This module does not have a public interface. Use Proc::Background.


Proc::Background::Win32 - Implementation of process management for Win32 systems


Perl Fork Limitations

When Perl is built as a native Win32 application, the fork and exec are a broken approximation of their Unix counterparts. Calling fork creates a thread instead of a process, and there is no way to exit the thread without running Perl cleanup code, which could damage the parent in unpredictable ways, like closing file handles. Calling POSIX::_exit will kill both parent and child (the whole process), and even calling exec in the child still runs global destruction. File handles are shared between parent and child, so any file handle redirection you perform in the forked child will affect the parent and vice versa.

In short, never call fork or exec on native Win32 Perl.

Command Line

This module implements background processes using Win32::Process, which uses the Windows API's concepts of CreateProcess, TerminateProces, WaitForSingleObject, GetExitCode, and so on.

Windows CreateProcess expects an executable name and a command line; breaking the command line into an argument list is left to each individual application, most of which use the library function CommandLineToArgvW. This module Win32::ShellQuote to parse and format Windows command lines.

If you supply a single-string command line, and don't specify the executable with the 'exe' option, it splits the command line and uses the first argument. Then it looks for that argument in the PATH, searching again with a suffix of ".exe" if the original wasn't found.

If you supply a command of multiple arguments, they are combined into a command line using Win32::ShellQuote. The first argument is used as the executable (unless you specified the 'exe' option), and gets the same path lookup.

Initial File Handles

When no options are specified, the new process does not inherit any file handles of the current process. This differs from the Unix implementation, but I'm leaving it this way for back-compat. If you specify any of stdin, stdout, or stderr, this module delivers them to the new process by temporarily redirecting STDIN, STDOUT, and STDERR of the current process, which the child process then inherits. Any handle not specified will be inherited as-is. If you wish to redirect a handle to NUL, set the option to undef:

  stdin  => undef,     # stdin will read from NUL device
  stdout => $some_fh,  # stdout will write to a file handle
  stderr => \*STDERR,  # stderr will go to the same STDERR of the current process


  • Blair Zajac <blair@orcaware.com>

  • Michael Conrad <mike@nrdvana.net>


version 1.30


This software is copyright (c) 2021 by Michael Conrad, (C) 1998-2009 by Blair Zajac.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.