Sending an arrow key with fprintf

Question

I'm testing out pipes and have hit a little road block.

I want to be able to simulate pressing the right arrow key through a file pointer opened by popen. The file pointer opens a display program on a different terminal, much like a projector. I would like to send a signal to advance the next image (the right arrow key).

How do I go about sending this signal? I realize this will be specific to my computer (BOIS/keyboard setup), but I'm not looking for this to be portable in anyway.

It seems from my trials, everything I send via fprintf is interpreted as readable characters rather than special codes.

The slideshow program cannot be changed, so that isn't an option. Any direction would be greatly appreciated.

You can try with `fwrite()` instead of `fprintf()` but I am not sure if it will work. — Iharob Al Asimi, May 17 '15 at 18:46
Pipes probably will not get where you want to go - the receiving program has to accept that style of input. — Thomas Dickey, May 17 '15 at 18:47
@ThomasDickey Is there alternative? I'm open to anything at this point. — Deanie, May 17 '15 at 18:48
To answer, we need more info, for example (a) what type of terminal, e.g., text or GUI, (b) are you trying to automate something or just control it. — Thomas Dickey, May 17 '15 at 18:51
@ThomasDickey (a) text, (b) Just control i. I don't care about a response. — Deanie, May 17 '15 at 19:11
You may try sending ANSI escape sequences (cursor back/forward)... but I think your chances in succeeding are pretty slim. — Lukas Thomsen, May 17 '15 at 19:11
[This link](http://stackoverflow.com/questions/12755968/sending-arrow-keys-to-popen?rq=1) claims to lead to something useful. If so, one of the pitfalls is that you probably have to do frequent fflush's to make it work. — Thomas Dickey, May 17 '15 at 20:01
@ThomasDickey That last link was what I needed. This is perfect. ty. Post it as an answer, and I'll select it. — Deanie, May 18 '15 at 05:13

score 1 · Accepted Answer · edited May 23 '17 at 11:58

Two possibilities come to mind:

The expect program can be used to control terminal applications. Its wiki shows An example wherein Expect controls a pager.
On the other hand, the question Sending Arrow Keys to Popen claims to lead to something useful. In particular, note the accepted answer, pointing to How to send UP arrow key to popen child, which sends the literal escape sequence for the arrow key via the pipe.

From the comments, that appears to be what was requested. Arrow (cursor) key escape sequences are well-standardized, as shown in

Bash Prompt HOWTO: Chapter 6. ANSI Escape Sequences: Colours and Cursor Movement
VT100.net: VT100 User Guide: Chapter 3. Programmer Information, e.g., CUF (cursor forward).

If that works for you, one of the pitfalls is that you probably have to do frequent fflush's to make it work.

I spoke too soon, this solution didn't work in the final environment, just in my initial test environment. — Deanie, May 19 '15 at 04:49

Sending an arrow key with fprintf

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