PHP command line scripting multiple process forking

I have been playing with this for a couple of days and have run into a few issues: I am wanting to run a set number of multiple processes (ie 25 at a time). I can't use the exec command since it will not wait for the output (this is a delayed response - network based). $cmd = "/path.to/some.cmd"; $options = "--options"; $lines = file (/path.to/some.file); while (list ($line_num, $line) = each ($lines)) { $trimline = trim ($line); shell_exec ("$cmd $options $trimline &"); } This works but I want to fork it multiple times and have a set number of lines running at a time. Anyone have any ideas? Thank you, Roy Walker