redhat man page for apache::subprocess

SUBPROCESS(1)						User Contributed Perl Documentation					     SUBPROCESS(1)

NAME
       Apache::SubProcess -- Executing SubProcesses from mod_perl

SYNOPSIS
	 use Apache::SubProcess ();

	 use Config;
	 use constant PERLIO_IS_ENABLED => $Config{useperlio};

	 # pass @ARGV / read from the process
	 $command = "/tmp/argv.pl";
	 @argv = qw(foo bar);
	 $out_fh = Apache::SubProcess::spawn_proc_prog($r, $command, @argv);
	 $output = read_data($out_fh);

	 # pass environment / read from the process
	 $command = "/tmp/env.pl";
	 $r->subprocess_env->set(foo => "bar");
	 $out_fh = Apache::SubProcess::spawn_proc_prog($r, $command);
	 $output = read_data($out_fh);

	 # write to/read from the process
	 $command = "/tmp/in_out_err.pl";
	 ($in_fh, $out_fh, $err_fh) =
	     Apache::SubProcess::spawn_proc_prog($r, $command);
	 print $in_fh "hello
";
	 $output = read_data($out_fh);
	 $error  = read_data($err_fh);

	 # helper function to work w/ and w/o perlio-enabled Perl
	 sub read_data {
	     my($fh) = @_;
	     my $data;
	     if (PERLIO_IS_ENABLED || IO::Select->new($fh)->can_read(10)) {
		 $data = <$fh>;
	     }
	     return defined $data ? $data : '';
	 }

DESCRIPTION
       "Apache::SubProcess" provides the Perl API for running and communicating with processes spawned from mod_perl handlers.

API
       spawn_proc_prog()

	 $out_fh =
	     Apache::SubProcess::spawn_proc_prog($r, $command, [@argv]);
	 ($in_fh, $out_fh, $err_fh) =
	     Apache::SubProcess::spawn_proc_prog($r, $command, [@argv]);

       spawn_proc_prog() spawns a sub-process which exec()'s $command and returns the output pipe filehandle in the scalar context, or input, out-
       put and error pipe filehandles in the list context. Using these three pipes it's possible to communicate with the spawned process.

       The third optional argument is a reference to an array which if passed becomes ARGV to the spawned program.

       It's possible to pass environment variables as well, by calling:

	 $r->subprocess_env->set($key => $value);

       before spawning the subprocess.

       There is an issue with reading from the read filehandle ($in_fh)):

       A pipe filehandle returned under perlio-disabled Perl needs to call select() if the other end is not fast enough to send the data, since
       the read is non-blocking.

       A pipe filehandle returned under perlio-enabled Perl on the other hand does the select() internally, because it's really a filehandle
       opened via ":APR" layer, which internally uses APR to communicate with the pipe. The way APR is implemented Perl's select() cannot be used
       with it (mainly because select() wants fileno() and APR is a crossplatform implementation which hides the internal datastructure).

       Therefore to write a portable code, you want to use select for perlio-disabled Perl and do nothing for perlio-enabled Perl, hence you can
       use something similar to the read_data() wrapper shown in the SYNOPSIS section.

perl v5.8.0							    2002-09-02							     SUBPROCESS(1)