you can try the following solution as well:
chmod +x post.php
chmod +x bash.sh
echo "* * * * * /home/samitha/bash.sh >> /home/samitha/log/cron.log 2>&1" >> cronjob
chmod +x cronjob
/etc/init.d/crond start #redhat based servers like centos
/etc/init.d/cron start #debian based servers like ubuntu
crontab cronjob