AnyEvent::Open3::Simple - Interface to open3 under AnyEvent


version 0.90


 use 5.010;
 use AnyEvent;
 use AnyEvent::Open3::Simple;
 my $done = AnyEvent->condvar;
 my $ipc = AnyEvent::Open3::Simple->new(
   on_start => sub {
     my $proc = shift;       # isa AnyEvent::Open3::Simple::Process
     my $program = shift;    # string
     my @args = @_;          # list of arguments
     say 'child PID: ', $proc->pid;
   on_stdout => sub {
     my $proc = shift;       # isa AnyEvent::Open3::Simple::Process
     my $line = shift;       # string
     say 'out: ', $string;
   on_stderr => sub {
     my $proc = shift;       # isa AnyEvent::Open3::Simple::Process
     my $line = shift;       # string
     say 'err: ', $line;
   on_exit   => sub {
     my $proc = shift;       # isa AnyEvent::Open3::Simple::Process
     my $exit_value = shift; # integer
     my $signal = shift;     # integer
     say 'exit value: ', $exit_value;
     say 'signal:     ', $signal;
   on_error => sub {
     my $error = shift;      # the exception thrown by IPC::Open3::open3
     my $program = shift;    # string
     my @args = @_;          # list of arguments
     warn "error: $error";
 $ipc->run('echo', 'hello there');


This module provides an interface to open3 while running under AnyEvent that delivers data from stdout and stderr as lines are written by the subprocess. The interface is reminiscent of IPC::Open3::Simple, although this module does provides a somewhat different API, so it cannot be used a drop in replacement for that module.

There are already a number of interfaces for interacting with subprocesses in the context of AnyEvent, but this one is the most convenient for my usage. Note the modules listed in the SEE ALSO section below for other interfaces that may be more or less appropriate.


Constructor takes a hash or hashref of event callbacks and attributes. Event callbacks have an on_ prefix, attributes do not.


  • implementation

    The implementation to use for detecting process termination. This should be one of child, idle or mojo. On all platforms except for Microsoft Windows (but not Cygwin) the default is child.

    You can change the default by setting the ANYEVENT_OPEN3_SIMPLE environment variable, like this:

     % export ANYEVENT_OPEN3_SIMPLE=idle

    The mojo implementation is experimental and allows you to use AnyEvent::Open3::Simple with Mojolicious but without EV (which is usually required for AnyEvent, Mojolicious interaction).


These events will be triggered by the subprocess when the run method is called. Each event callback (except on_error) gets passed in an instance of AnyEvent::Open3::Simple::Process as its first argument which can be used to get the PID of the subprocess, or to write to it. on_error does not get a process object because it indicates an error in the creation of the process.

Not all of these events will fire depending on the execution of the child process. In the very least exactly one of on_start or on_error will be called.

  • on_start ($proc, $program, @arguments)

    Called after the process is created, but before the run method returns (that is, it does not wait to re-enter the event loop first).

    In versions 0.78 and better, this event also gets the program name and arguments passed into the run method.

  • on_error ($error, $program, @arguments)

    Called when there is an execution error, for example, if you ask to run a program that does not exist. No process is passed in because the process failed to create. The error passed in is the error thrown by IPC::Open3 (typically a string which begins with "open3: ...").

    In some environments open3 is unable to detect exec errors in the child, so you may not be able to rely on this event. It does seem to work consistently on Perl 5.14 or better though.

    Different environments have different ways of handling it when you ask to run a program that doesn't exist. On Linux and Cygwin, this will raise an on_error event, on MSWin32 it will not trigger a on_error and instead cause a normal exit with a exit value of 1.

    In versions 0.77 and better, this event also gets the program name and arguments passed into the run method.

  • on_stdout ($proc, $line)

    Called on every line printed to stdout by the child process.

  • on_stderr ($proc, $line)

    Called on every line printed to stderr by the child process.

  • on_exit ($proc, $exit_value, $signal)

    Called when the processes completes, either because it called exit, or if it was killed by a signal.

  • on_success ($proc)

    Called when the process returns zero exit value and is not terminated by a signal.

  • on_signal ($proc, $signal)

    Called when the processes is terminated by a signal.

  • on_fail ($proc, $exit_value)

    Called when the process returns a non-zero exit value.



 $ipc->run($program, @arguments);
 $ipc->run($program, @arguments, \$stdin);             # (version 0.76)
 $ipc->run($program, @arguments, \@stdin);             # (version 0.76)
 $ipc->run($program, @arguments, sub {...});           # (version 0.80)
 $ipc->run($program, @arguments, \$stdin, sub {...});  # (version 0.80)
 $ipc->run($program, @arguments, \@stdin, sub {...});  # (version 0.80)

Start the given program with the given arguments. Returns immediately. Any events that have been specified in the constructor (except for on_start) will not be called until the process re-enters the event loop.

You may optionally provide the full content of standard input as a string reference or list reference as the last argument (or second to last if you are providing a callback below). If provided as a list reference, it will be joined by new lines in whatever format is native to your Perl. Currently on (non cygwin) Windows (Strawberry, ActiveState) this is the only way to provide standard input to the subprocess.

Do not mix the use of passing standard input to run and AnyEvent::Open3::Simple::Process#print or AnyEvent::Open3::Simple::Process#say, otherwise bad things may happen.

In version 0.80 or better, you may provide a callback as the last argument which is called before on_start, and takes the process object as its only argument. For example:

 foreach my $i (1..10)
   $ipc->run($prog, @args, \$stdin, sub {
     my($proc) = @_;
     $proc->user({ iteration => $i });

This is useful for making data accessible to $ipc object's callbacks that may be out of scope otherwise.


Some AnyEvent implementations may not work properly with the method used by AnyEvent::Open3::Simple to wait for the child process to terminate. See "CHILD PROCESS WATCHERS" in AnyEvent for details.

This module uses an idle watcher instead of a child watcher to detect program termination on Microsoft Windows (but not Cygwin). This is because the child watchers are unsupported by AnyEvent on Windows. The idle watcher implementation seems to pass the test suite, but there may be some traps for the unwary. There may be other platforms or event loops where this is the appropriate choice, and you can use the ANYEVENT_OPEN3_SIMPLE environment variable or the implementation attribute to force it use an idle watcher instead. Patches for detecting environments where idle watchers should be used are welcome and encouraged.

As of version 0.85, this module works on Windows with AnyEvent::Impl::EV, AnyEvent::Impl::Event and AnyEvent::Impl::Perl (possibly others), although in the past they have either not worked or had limitations placed on them. Because the author of AnyEvent does not hold the native Windows port of Perl in high regard: problems such as this may pop up again in the future and may not be addressed, and may be out of the control of the author of this module.

Performance for the idle watcher implementation on native Windows (non-Cygwin) is almost certainly suboptimal, but the author of this module uses it and finds it useful despite this.

Writing to a subprocesses stdin with AnyEvent::Open3::Simple::Process#print or AnyEvent::Open3::Simple::Process#say is unsupported on Microsoft Windows (it does work under Cygwin though).

There are some traps for the unwary relating to buffers and deadlocks, IPC::Open3 is recommended reading.

If you register a call back for on_exit, but not on_error then use a condition variable to wait for the process to complete as in this:

 my $cv = AnyEvent->condvar;
 my $ipc = AnyEvent::Open3::Simple->new(
   on_exit => sub { $cv->send },

You might be waiting forever if there is an error starting the process (if for example you give it a bad command). To handle this situation you might use croak on the condition variable in the event of error:

 my $cv = AnyEvent->condvar;
 my $ipc = AnyEvent::Open3::Simple->new(
   on_exit => sub { $cv->send },
   on_error => sub {
     my $error = shift;

This will cause the recv to die, printing a useful diagnostic if the exception isn't caught somewhere else.



Represents a process being run by this module, typically passed into the callbacks.


Alternative to this module.


Alternative to this module.


Author: Graham Ollis <>


Stephen R. Scaffidi

Scott Wiersdorf

Graham Knop (HAARG)


This software is copyright (c) 2012-2022 by Graham Ollis.

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