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

       Apache::SubProcess -- Executing SubProcesses from mod_perl

         use Apache::SubProcess ();

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

         # pass @ARGV / read from the process
         $command = "/tmp/";
         @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/";
         $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_fh, $out_fh, $err_fh) =
             Apache::SubProcess::spawn_proc_prog($r, $command);
         print $in_fh "hello\n";
         $output = read_data($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 : '';

       "Apache::SubProcess" provides the Perl API for running and communicat-
       ing with processes spawned from mod_perl handlers.


         $out_fh =
             Apache::SubProcess::spawn_proc_prog($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,
       output 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 sec-

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