Problem with feeding password while changing to root user

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http://www.unix.com – i want to change user to "root" from another user while running a script. how can i automatically feed the password? for example, i want to write a script say "script.sh"... it will first run the command "p" as mhmn user, and then it will change the user to "root" by using "su - root" command. at this point it asks for the password for root. say the password is "blue". i want to feed the p.w. automatically while it asks for it. inside script.sh it will look something like- Code: #p #su - root (feed p.w. automatically here) #p (HowTos)