How can I pipe initial input into process which will then be interactive?

Question

I\'d like to be able to inject an initial command into the launching of an interactive process, so that I can do something like this:

echo \"initial command\         


        

Answer 1

This is easy to do with the program "expect" which is intended to let you write scripts to interact with programs.

I tested this by writing an expect script bc.exp to launch the calculator "bc" and send it the command "obase=16" to put it into hexadecimal output mode, and then turn over control to me.

The script (in a file named bc.exp) is

spawn bc
send "obase=16\n"
interact {
 \003 exit
}

One runs it with

expect bc.exp