backup a database

[Rafael Diaz Valdes]

Hi,
 
 I 'm using mysqldump to backup my database, I wrote in my backup.sh the 
following string: 
 
$MYSQL/bin/mysqldump --opt databasename -user=root --password=rootpassword > 
backup/mysql/databasename.sql
 
I include backup.sh in my cron weekly (/etc/cron.weekly) but when it is 
executed  appear databasename.sql empty, else if I run backup.sh in a shell 
konsole it is executed ok,
 
do you know why can not execute the string in the cron ?? 
 
my mysql version is : 4.0.17 
 
regards rafael