shell script not working with shell_exec

Hi, I have a shell script which works when executed from the command line, but doesn't when executed from PHP with shell_exec. Of course I realize that in the former case I am 'root' and in the latter 'apache', so I changed every involved file to have the owner:group apache:apache and also the permissions on the directories. Without success ... There are two commands: shell_exec("/root/MBROLA/txt2pho/d/txt2pho/txt2pho < /var/www/html/museum/audio/TTS_1.txt > /var/www/html/museum/audio/TTS_1.pho"); shell_exec("/root/MBROLA/mbrola-linux-i386 /root/MBROLA/voices/d/de3/de3 /var/www/html/museum/audio/TTS_1.pho /var/www/html/museum/audio/TTS_1.wav"); As I installed the txt2pho and mbrola packages under uid root, there are probably 2 options left: 1. reinstall these packages under uid apache (? - how can I login as apache ?) 2. change the shell_exec uid from apache to root (? - dangerous probably, I read something about using sudo ?) I'm quite stuck now how to proceed. Any help is welcome, Chris.