Prepend to stdin

Question

I've got an interactive command line program that we'll call program.exe. While it's running, I can type in a bunch of different commands that do different things. We'll call them: doA, doB, doC, and quit. Now, as it turns out, the first thing I want to do in program.exe is always doA. I'd like to save a few keystrokes and automatically have program.exe run the command doA upon startup. Unfortunately, I can't just pass "doA" on the command line because whoever created program.exe didn't implement that feature.

The way I see it, I have a few options:

• Write another program that calls program.exe, writes doA to its stdin, then hooks it's own stdin to program.exe's stdin and hooks program.exe's sdtout to it's own stdout. This will probably work, but I'd like to see if there's a solution that doesn't require a compiler

• Use some batch file magic to jam doA into program.exe's stdin. This is the part that I've got questions about. Here's what I've tried so far:

echo doA | program.exe

This works, in that program.exe executes doA, but then I can't type any other commands to program.exe. Echo is hogging up program.exe's stdin

more | echo doA | program.exe

This also works and gets a little closer to what I'm after. program.exe executes doA and I see the output from doA. I can also type in additional commands, but I don't see the output from these commands. Furthermore, when I send the quit command, program.exe terminates (I guess), but I'm still stuck in the "more" command and I can keep typing lines until I hit ctrl+c.

The Question: Is there another way to do what I'm trying to do with a bat file? Conceptually, I think I need to combine two streams (the keyboard, and the literal "doA") into one and pass that into program.exe, but I could be way off.

Answer 1

First, more | echo doA | program.exe does not do what you think it does. After sending doA echo does not connect those pipe stages together, it rather creates perfect sink - that's why you do not see your commands echoed. They go nowhere and are not executed by program.exe. I don't think there is a simple way to achieve what you want directly from command line, but it can be easily resolved by using small batch file. Create a batch file, say args.bat:

@echo off 
echo First command
more

Now run your program by args|program.exe