running php script daily at fixed time

i have prepared a php script which takes input from a database and sends it to certain email addresses. this script is working when i manually execute it. i want to execute it daily at a fixed time ...so that the whole process is automated. i am running this on a red hat kinux server with apache running. at present i have tried to run it thru shell script (editing crontab)but the shell script does not recognise a php file. what is the alternative? any help would be greatly appreciated. thanks please reply to shabbardaud@hotmail.com shabbar