You can call other programs from within your program with the system() function or by using back ticks ``.

As for being able to read/write to the program you have called you'll want to take a look at the documentation for open(), open2(), and open3() depending on what you are trying to accomplish.

If you could give us some more detailed information we'd be able to help you further.

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Frank Wiles <frank@wiles.org>
http://frank.wiles.org