Proc::Simple -- launch and control background processes

NOTE
REQUIREMENTS
AUTHOR

NAME

Proc::Simple -- launch and control background processes

SYNOPSIS

   use Proc::Simple;

   $myproc = Proc::Simple->new();        # Create a new process object

   $myproc->start("shell-command-line"); # Launch an external program
   $myproc->start("command",             # Launch an external program
                  "param", ...);         # with parameters


   $myproc->start(sub { ... });          # Launch a perl subroutine
   $myproc->start(\&subroutine);         # Launch a perl subroutine
   $myproc->start(\&subroutine,          # Launch a perl subroutine
                  $param, ...);          # with parameters

   $running = $myproc->poll();           # Poll Running Process

   $proc->kill_on_destroy(1);            # Set kill on destroy
   $proc->signal_on_destroy("KILL");     # Specify signal to be sent
                                         # on destroy

   $myproc->kill();                      # Kill Process (SIGTERM)

   $myproc->kill("SIGUSR1");             # Send specified signal

   $myproc->exit_status();               # Return exit status of process

   Proc::Simple::debug($level);          # Turn debug on

DESCRIPTION

The Proc::Simple package provides objects mimicing real-life processes from a user's point of view. A new process object is created by

   $myproc = Proc::Simple->new();

Either external programs or perl subroutines can be launched and controlled as processes in the background.

A 10-second sleep process, for example, can be launched as an external program as in

   $myproc->start("/bin/sleep 10");    # or
   $myproc->start("/bin/sleep", "10");

or as a perl subroutine, as in

   sub mysleep { sleep(shift); }    # Define mysleep()
   $myproc->start(\&mysleep, 10);   # Launch it.

or even as

   $myproc->start(sub { sleep(10); });

The start Method returns immediately after starting the specified process in background, i.e. there's no blocking. It returns 1 if the process has been launched sucessfully and 0 if not.

The poll method checks if the process is still running

   $running = $myproc->poll();

and returns 1 if it is, 0 if it's not. Finally,

   $myproc->kill();

terminates the process by sending it the SIGTERM signal. As an option, another signal can be specified.

   $myproc->kill("SIGUSR1");

sends the SIGUSR1 signal to the running process. kill returns 1 if it succeeds in sending the signal, 0 if it doesn't.

The methods are discussed in more detail in the next section.

A destructor is provided so that a signal can be sent to the forked processes automatically should the process object be destroyed or if the process exits. By default this behaviour is turned off (see the kill_on_destroy and signal_on_destroy methods).

METHODS

The following methods are available:

new (Constructor)

Create a new instance of this class by writing

  $proc = new Proc::Simple;

  $proc = Proc::Simple->new();

It takes no arguments.

start

Launches a new process. The start() method can be used to launch both external programs (like /bin/echo) or one of your self-defined subroutines (like foo()) in a new process.

Starting External Programs

For an external program to be started, call

 $status = $proc->start("program-name");

If you want to pass a couple of parameters to the launched program, there's two options: You can either pass them in one argument like in

 $status = $proc->start("/bin/echo hello world");

or in several arguments like in

 $status = $proc->start("/bin/echo", "hello", "world");

Just as in Perl's function system(), there's a big difference between the two methods: If you provide one argument containing a blank-separated command line, your shell is going to process any meta-characters (if you choose to use some) before the process is actually launched:

 $status = $proc->start("/bin/ls -l /etc/initt*");

will expand /etc/initt* to /etc/inittab before running the ls command. If, on the other hand, you say

 $status = $proc->start("/bin/ls", "-l", "*");

the * will stay unexpanded, meaning you'll look for a file with the literal name * (which is unlikely to exist on your system unless you deliberately create confusingly named files :). For more info on this, look up perldoc -f exec.

Starting Subroutines

If, on the other hand, you want to start a Perl subroutine in the background, simply provide the function reference like

 $status = $proc->start(\&your_function);

or supply an unnamed subroutine:

 $status = $proc->start( sub { sleep(1) } );

You can also provide additional parameters to be passed to the function:

 $status = $proc->start(\&printme, "hello", "world");

The start Method returns immediately after starting the specified process in background, i.e. non-blocking mode. It returns 1 if the process has been launched sucessfully and 0 if not.

poll

The poll method checks if the process is still running

   $running = $myproc->poll();

and returns 1 if it is, 0 if it's not.

kill

The kill() method:

   $myproc->kill();

terminates the process by sending it the SIGTERM signal. As an option, another signal can be specified.

   $myproc->kill("SIGUSR1");

sends the SIGUSR1 signal to the running process. kill returns 1 if it succeeds in sending the signal, 0 if it doesn't.

kill_on_destroy

Set a flag to determine whether the process attached to this object should be killed when the object is destroyed. By default, this flag is set to false. The current value is returned.

  $current = $proc->kill_on_destroy;
  $proc->kill_on_destroy(1); # Set flag to true
  $proc->kill_on_destroy(0); # Set flag to false

signal_on_destroy

Method to set the signal that will be sent to the process when the object is destroyed (Assuming kill_on_destroy is true). Returns the current setting.

  $current = $proc->signal_on_destroy;
  $proc->signal_on_destroy("KILL");

redirect_output

This allows to redirect the stdout and/or stderr output to a file. Specify undef to leave th

  # stdout to a file, left stderr unchanged
  $proc->redirect_output ("/tmp/someapp.stdout", undef);


  # stderr to a file, left stdout unchanged
  $proc->redirect_output (undef, "/tmp/someapp.stderr");


  # stdout and stderr to a separate file
  $proc->redirect_output ("/tmp/someapp.stdout", "/tmp/someapp.stderr");

Call this method before running the start method.

pid

Returns the pid of the forked process associated with this object

  $pid = $proc->pid;

DESTROY (Destructor)

Object destructor. This method is called when the object is destroyed (eg with ``undef'' or on exiting perl). If kill_on_destroy is true the process associated with the object is sent the signal_on_destroy signal (SIGTERM if undefined).

exit_status

Returns the exit status of the process as the $! variable indicates. If the process is still running, undef is returned.

debug

Switches debug messages on and off -- Proc::Simple::debug(1) switches them on, Proc::Simple::debug(0) keeps Proc::Simple quiet.

NOTE

Please keep in mind that there is no guarantee that the SIGTERM signal really terminates a process. Processes can have signal handlers defined that avoid the shutdown. If in doubt, whether a process still exists, check it repeatedly with the poll routine after sending the signal.

REQUIREMENTS

I'd recommend using perl 5.6.0 although it might also run with 5.003 -- if you don't have it, this is the time to upgrade!

AUTHOR

Michael Schilli <michael@perlmeister.com>

Contributors:

Tim Jenness <t.jenness@jach.hawaii.edu> did kill_on_destroy/signal_on_destroy/pid

Mark R. Southern <mark_southern@merck.com> worked on EXIT_STATUS tracking

Tobias Jahn <tjahn@users.sourceforge.net> added redirection to stdout/stderr

Clauss Strauch <Clauss_Strauch@aquila.fac.cs.cmu.edu> suggested the multi-arg start()-methods.

Proc::Simple -- launch and control background processes