Michelangelo van Dam has a quick new post to his site talking about popen and pipes in command-line PHP as an alternative to the "exec" functions PHP provides to make command lines calls.
I got a question today about using commands that pipe output to other commands within PHP applications. There are two functions in PHP that are perfect for the task: popen and proc_open. But when you want to run it as a complete process, you can go about using exec, shell_exec, passthru or system and fiddle with escapeshellcmd. But often this looks messy and not reusable. A better approach would be to use "popen".
He includes a code example of how to use this method, showing a call to a command line tool and piping the results back into a PHP variable for later use. You can find out more about the use of popen in the PHP manual and accompanying examples.