Oracle 8.0.6
Compaq Tru64 4.0D

I am trying to RMAN backup job from cron.
The shell script I wrote works fine when run interactively but doesn't work when scheduled through cron. The log file, to which I am directing the output of the shell comes blank.
I suspect I am missing some environment variables but don't know which one? Below are my shell script and rman script.

export ORABIN=/ora01/app/oracle/product/8.0.6/bin
export PATH=.:/ora01/app/oracle/product/8.0.6/bin:/opt/bin:/bin:/usr/bin:/usr/ccs/bin:/usr/local/bin
export ORACLE_BASE=/ora01/app/oracle
export ORACLE_SID=fdbsp
export LD_LIBRARY_PATH=/ora01/app/oracle/product/8.0.6/lib:/usr/lib
export ORACLE_HOME=/ora01/app/oracle/product/8.0.6
/ora01/app/oracle/product/8.0.6/bin/rman target sys/password@fdbsp rcvcat rman/rman@catlg cmdfile /ora01/app/oracle/cron/backup_ful
l_db.rman msglog /ora01/app/oracle/cron/output/backup_full_db.log
run {execute script backup_full_db_al_disk;}
Any idea? Appreciate all help.