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Mojo::Run3 - Run a subprocess and read/write to it


  use Mojo::Base -strict, -signatures;
  use Mojo::Run3;

This example gets "stdout" events when the "ls" command emits output:

  use IO::Handle;
  my $run3 = Mojo::Run3->new;
  $run3->on(stdout => sub ($run3, $bytes) {

  $run3->run_p(sub { exec qw(/usr/bin/ls -l /tmp) })->wait;

This example does the same, but on a remote host using ssh:

  my $run3 = Mojo::Run3->new->driver({pty => 1, pipe => 1}});

  $run3->once(pty => sub ($run3, $bytes) {
    $run3->write("my-secret-password\n", "pty") if $bytes =~ /password:/;

  $run3->on(stdout => sub ($run3, $bytes) {

  $run3->run_p(sub { exec qw(ssh ls -l /tmp) })->wait;


Mojo::Run3 allows you to fork a subprocess which you can write STDIN to, and read STDERR and STDOUT without blocking the the event loop.

This module also supports IO::Pty which allows you to create a pseudoterminal for the child process. This is especially useful for application such as bash and ssh.

This module is currently EXPERIMENTAL, but unlikely to change much.



  $run3->on(drain => sub ($run3) { });

Emitted after "write" has written the whole buffer to the subprocess.


  $run3->on(error => sub ($run3, $str) { });

Emitted when something goes wrong.


  $run3->on(finish => sub ($run3, @) { });

Emitted when the subprocess has ended. "error" might be emitted before "finish", but "finish" will always be emitted at some point after "start" as long as the subprocess actually stops. "status" will contain $! if the subprocess could not be started or the exit code from the subprocess.


  $run3->on(pty => sub ($run3, $bytes) { });

Emitted when the subprocess write bytes to IO::Pty. See "driver" for more details.


  $run3->on(stderr => sub ($run3, $bytes) { });

Emitted when the subprocess write bytes to STDERR.


  $run3->on(stdout => sub ($run3, $bytes) { });

Emitted when the subprocess write bytes to STDOUT.


  $run3->on(spawn => sub ($run3, @) { });

Emitted in the parent process after the subprocess has been forked.



  $hash_ref = $run3->driver;
  $run3 = $run3->driver({stdin => 'pipe', stdout => 'pipe', stderr => 'pipe'});

Used to set the driver for "pty", "stdin", "stdout" and "stderr". The "pipe" key is a shortcut for setting "stdin", "stdout" and "stderr" to "pipe" unless specified.


  # Open pipe for STDIN and STDOUT and close STDERR in child process
  $run3->driver({pipe => 1, stderr => 'close'});

  # Create a PTY and attach STDIN to it and open a pipe for STDOUT and STDERR
  $run3->driver({stdin => 'pty', stdout => 'pipe', stderr => 'pipe'});

  # Create a PTY and pipes for STDIN, STDOUT and STDERR
  $run3->driver({pty => 1, stdin => 'pipe', stdout => 'pipe', stderr => 'pipe'});

  # Create a PTY, and require the slave to to be manually closed
  $run3->driver({pty => 1, stdout => 'pipe', close_slave => 0});

  # Create a PTY, but do not make the PTY slave the controlling terminal
  $run3->driver({pty => 1, stdout => 'pipe', make_slave_controlling_terminal => 0});


  $ioloop = $run3->ioloop;
  $run3   = $run3->ioloop(Mojo::IOLoop->singleton);

Holds a Mojo::IOLoop object.



  $int = $run3->bytes_waiting;

Returns how many bytes has been passed on to "write" buffer, but not yet written to the child process.


  $run3 = $run3->close($conduit);

Used to close open filehandles. This method can be called in both parent and child process. $conduit can be:

  • stdin, stdout, stderr

    Close STDIN, STDOUT or STDERR in parent or child process. Closing "stdin" is useful after piping data into a process like cat.

  • pty, slave

    If "driver" opens a "pty", there will be one filehandle opened for the child and one for the parent. The actual "pty" can be closed in both parent and child, while the "slave" can only be closed from the parent process if close_slave was set to "0" (zero) in "driver".

  • other

    This is useful in the child process to close every filehandle that is not STDIN, STDOUT or STDERR. This is required when opening programs that does not automatically do this for you, like "telnet":

      $run3->start(sub ($run3, @) {
        exec telnet => '';


  $int = $run3->exit_status;

Returns the exit status part of "status", which will should be a number from 0 to 255.


  $fh = $run3->handle($name);

Returns a file handle or undef for $name, which can be "stdin", "stdout", "stderr" or "pty". This method returns the write or read "end" of the file handle depending if it is called from the parent or child process.


  $int = $run3->kill($signal);

Used to send a $signal to the subprocess. Returns -1 if no process exists, 0 if the process could not be signalled and 1 if the signal was successfully sent.


  $int = $run3->pid;

Process ID of the child after "start" has successfully started. The PID will be "0" in the child process and "-1" before the child process was started.


  $p = $run3->run_p(sub ($run3) { ... })->then(sub ($run3) { ... });

Will "start" the subprocess and the promise will be fulfilled when "finish" is emitted.


  $run3 = $run3->start(sub ($run3, @) { ... });

Will start the subprocess. The code block passed in will be run in the child process. exec() can be used if you want to run another program. Example:

  $run3 = $run3->start(sub { exec @my_other_program_with_args });
  $run3 = $run3->start(sub { exec qw(/usr/bin/ls -l /tmp) });


  $int = $run3->status;

Holds the exit status of the program or $! if the program failed to start. The value includes signals and coredump flags. "exit_status" can be used instead to get the exit value from 0 to 255.


  $run3 = $run3->write($bytes);
  $run3 = $run3->write($bytes, sub ($run3) { ... });
  $run3 = $run3->write($bytes, $conduit);
  $run3 = $run3->write($bytes, $conduit, sub ($run3) { ... });

Used to write $bytes to the subprocess. $conduit can be "pty" or "stdin", and defaults to "stdin". The optional callback will be called on the next "drain" event.


Jan Henning Thorsen


This program is free software, you can redistribute it and/or modify it under the terms of the Artistic License version 2.0.

SEE ALSO, Mojo::Run3::Util, Mojo::IOLoop::ReadWriteFork, IPC::Run3.