AIX

As you might need this for other occasions here is how you do it:

Short introduction to I/O redirection

You can picture any process in UNIX to be like a garden hose: something goes in on top, something goes out on the bottom. You can daisy-chain processes in a pipeline with the "|"-symbol, which simply means "connect the output of one process with the input of the other".

Now suppose you want to produce a "y". You could use (try out the following out, it is all non-descructive):

Code:

print - "y"

So this is a process which takes nothing in and sends something (a "y") to its output. Let us construct a process processing some input (we could use your compress-process, but we want something we can watch more closely):

Code:

#! /bin/ksh

typeset input=""
while : ; do
     input=""
     echo "enter something: " ; read input
     case $input in
          y)
               echo "you entered a 'y'. Exiting...."
               exit
               ;;
          *)
               echo "you entered '$input'. Enter 'y' to exit."
               ;;
     esac
done

Save this to a file "logger.ksh" and make it executable. Try it out on its own (it can be tricked by keyboard artistics like CTRL-C, but enter something "normal" and it does what you would expect - exit on "y" and start over on anything else).

Now call

Code:

 print - "y\n" | ./logger.ksh

and you will notice that this is the same as if you would have entered it by keyboard. Lets do another test. In case you wonder about the "\n" - these are just codes for the ENTER-key on your keyboard:

Code:

# print - "a\nb\ny\n" | ./logger.ksh
enter something: 
you entered 'a'. Enter 'y' to exit.
enter something: 
you entered 'b'. Enter 'y' to exit.
enter something: 
you entered a 'y'. Exiting....

Per default the input of a process is taken from the keyboard - like the shell (which is just another process), which listens there and takes up what you type. But by redirecting the input you can make the process take its input from any other source, just like you can make it put its output to somewhere else (like a file) instead of the screen it would normally output to. You can even use a file for input:

Code:

process < /path/to/some/file

To stay in the garden-hose picture i used above: you plug the respective end of the hose to some device, which can provide/store something to put through the hose - files, devices (like keyboards for input, screens for output) or other processes.

I hope this helps.

bakunin