发布shell并在php中忘记它

Question

how do you issue commands to the shell and then forget it's output and such? for example:

<?php
echo `sleep 2;echo hi`;
echo "foo";
?>

the result for this is hifoo. i would want a result that gives me foohi. why? i want the command issued to the shell simply issued and forgotten, i am confused about why PHP will wait for the result. is such a result possible?

(the idea behind this is setting up the correct number of selenium grid RC instances programatically. currently, it will stop after the first process is opened)

Answer 1

From php.net exec()

If a program is started with this function, in order for it to continue running in the background, the output of the program must be redirected to a file or another output stream. Failing to do so will cause PHP to hang until the execution of the program ends.

The same applies for all shell commands.