Basic question - Starting a background task without waiting for its end.

I (very simply) try to open a "notepad" on a simple text file in a simplistic PHP script, and would like to go on and display the next page without waiting for this notepad to be shut. After various attempts, I have used an : exec ('bash -c cmd /C start /MAX notepad "my_file" > NUL'); ... but it still wait for the shutting of the notepad ..! Could anybody help me ? For clarification : 1) I use this script on a machine which is in the same time "server" and "client", which gives "meaning" to this operation. 2) I use "bash -c" because I have the cygwin platform which can easily initiate tasks in background, but it could be suppressed, because it "de facto" changes nothing... Thank's for help. Michel.