An extension of IPC::Open3 that uses callbacks instead of filehandles
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IPC::Open3::Callback - An extension to IPC::Open3 that will feed out and err to callbacks instead of requiring the caller to handle them.


version 1.19


use IPC::Open3::Callback;
my $runner = IPC::Open3::Callback->new( {
    out_callback => sub {
        my $data = shift;
        my $pid = shift;

        print( "$pid STDOUT: $data\n" );
    err_callback => sub {
        my $data = shift;
        my $pid = shift;

        print( "$pid STDERR: $data\n" );
    } } );
my $exit_code = $runner->run_command( 'echo Hello World' );

use IPC::Open3::Callback qw(safe_open3);
my ($pid, $in, $out, $err) = safe_open3( "echo", "Hello", "world" ); 
$buffer = '';
my $select = IO::Select->new();
$select->add( $out );
while ( my @ready = $select->can_read( 5 ) ) {
    foreach my $fh ( @ready ) {
        my $line;
        my $bytes_read = sysread( $fh, $line, 1024 );
        if ( ! defined( $bytes_read ) && !$!{ECONNRESET} ) {
            die( "error in running ('echo $echo'): $!" );
        elsif ( ! defined( $bytes_read) || $bytes_read == 0 ) {
            $select->remove( $fh );
        else {
            if ( $fh == $out ) {
                $buffer .= $line;
            else {
                die( "impossible... somehow got a filehandle i dont know about!" );
waitpid( $pid, 0 );
my $exit_code = $? >> 8;
print( "$pid exited with $exit_code: $buffer\n" ); # 123 exited with 0: Hello World


This module feeds output and error stream from a command to supplied callbacks.
Thus, this class removes the necessity of dealing with IO::Select by hand and also provides a workaround for the bad reputation associated with Microsoft Windows' IPC.


safe_open3( $command, $arg1, ..., $argN )

Passes the command and arguments on to open3 and returns a list containing:

  • pid

    The process id of the forked process.

  • stdin

    An IO::Handle to STDIN for the process.

  • stdout

    An IO::Handle to STDOUT for the process.

  • stderr

    An IO::Handle to STDERR for the process.

As with open3, it is the callers responsibility to waitpid to ensure forked processes do not become zombies.

This method works for both *nix and Microsoft Windows OS's. On a Windows system, it will use sockets per

safe_open3_with( $in_handle, $out_handle, $err_handle, $command, $arg1, ..., $argN )

The same as safe_open3 except that you can specify the handles to be used instead of having safe_open3 generate them. Each handle can be undef. In fact, safe_open3 just calls safe_open3_with(undef, undef, undef, @command). The return values are the same except that undef will be returned for each handle corresponding to the same stream as a supplied handle. For example, if you specify an $out_handle then undef will be returned for the STDOUT handle.


new( \%options )

The constructor creates a new Callback object and optionally sets global callbacks for STDOUT and STDERR streams from commands that will get run by this object (can be overridden per call to run_command). The currently available options are:



set_buffer_output( $boolean )

A boolean value, if true, will buffer output and send to callback one line at a time (waits for '\n'). Otherwise, sends text in the same chunks returned by sysread.


set_buffer_size( $bytes )

The size of the read buffer (in bytes) supplied to sysread.


set_err_callback( &subroutine )

A subroutine that will be called for each chunk of text written to STDERR. The subroutine will be called with the same 2 arguments as out_callback.


The last command run by the run_command method.


The exit code of the last command run by the run_command method.


set_out_callback( &subroutine )

A subroutine that will be called whenever a chunk of output is sent to STDOUT by the opened process. The subroutine will be called with 2 arguments:

  • data

    A chunk of text written to the stream

  • pid

    The pid of the forked process


Will return the pid of the currently running process. This pid is set by run_command and will be cleared out when the run_command completes.


set_select_timeout( $seconds )

The timeout, in seconds, provided to IO::Select, by default 0 meaning no timeout which will cause the loop to block until output is ready on either STDOUT or STDERR.


run_command( $command, $arg1, ..., $argN, \%options )

Will run the specified command with the supplied arguments by passing them on to safe_open3. Arguments can be embedded in the command string and are thus optional.

If the last argument to this method is a hashref (ref(@_[-1]) eq 'HASH'), then it is treated as an options hash. The supported allowed options are the same as the constructor and will be used in preference to the values set by the
constructor or any of the setters. These options will be used for this single call, and will not modify the Callback object itself. run_command supports three additional options not supported by the constructor. They are:

  • in_handle

    An IO::Handle from which STDIN will be read.

  • out_handle

    An IO::Handle to which STDOUT will be written.

  • err_handle

    An IO::Handle to which STDERR will be written.

These handle options can be mixed with regular options and if multiple are specified on the same stream, the handle version will be used instead of the callback.

Returns the exit code from the command.



This software is copyright (c) 2013 by Lucas Theisen.

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


Please see those modules/websites for more information related to this module.