Below is the shell script, to be configured in crontab, which will send mail incase of blocking session observed in the database .
In the mail body it will contain the blocking sessions details also.

1. Prepare the blocker.sql file.[ for blocking sessions more than 10 seconds)

2. Shell script.(/home/oracle/monitor/blocker.sh )

You need to define the ORACLE_HOME,ORACLE_SID respectively.

3. configure in crontab( every one minute)