I thought of suPHP but that's not what I need. It doesn't serve to my purposes to run the whole PHP script as a different user. I just need to run one single linux command line as a different user.
Is it possible?
You could try the shell_exec function and sudo
edit: seeing as sudo prompts for a password, you'd might wanna use proc_open, which allows you to use pipes. See this comment for how to create a custom password pipe.