How to see Ruby error when called from PHP

I’m not seeing an error message when I call my Ruby script from PHP with

$s = sprintf(“ruby /Users/mark/scripts/myscript.rb >
/Users/mark/scripts/myscript.log &”);

I see print statements from my script in the log file, no errors.

The script is crashing on “requires ‘mysql’”

$LOAD_PATH << File.expand_path(File.dirname(FILE))
require ‘rubygems’
require ‘mysql’

I’m able to run the same script from crontab with the expand_path.

Any ideas?