Monitoring script for Log file

Hi,
Iam new to unix , plz help me to write below script.
I need to write a script for Monitoring log file when any error occurs it has to send a mail to specified users and it should be always pick latest error not the existing one and the script should be able to send mail all errors (more than one)

thank you

Who creates the log file? What kind of errors are you trying to capture? What is the OS you are running? Give more details pls.