i need a change password shell script for linux redhat

I need a linux shell script that will attempt to change a user password and if it doesnt , it will trap the error message returned by linux such as "Password to short or too long ".the shell script it would then store the result in a text file . I want to use the error msg and display it to the user so that user can try adn reenter a new password. the shell script would be called from a stored procedure like ("/home/[login to view URL] "||user||" "||old_password||" "||as_newpass);