Command Output to Standard Input

Hello,

How do I provide the output of a command to another command which is waiting for an input from the user ?

Ex : I need to login to a device via telnet. In the script, initially I use the "read" command to get the IP Address, Username and Password of the device from the user. Now, after issuing the telnet command in the script, I want to provide the username output read initially.

How would I do that ? Anyone help me out please with simple commands.

Thank You.