I am trying to capture input keys using this program.

I can write the output of the program to a file this way:
However the output is completely blank when put into a variable:
I have tried a large amount of variations of the above command. This is a little bit above the intensity level of programming I can understand. I would like to get back to doing more simple and understandable stuff than this. How can I fix this?

Hm. Would be nice to see what else did you try.
by the way probably that should be see man page (of xinput)

With or without the switch mark -- the command does the same. I have been using it without -- for a long time.

I think to write what I have tried here would just be more confusing because I tried some weird things. The way I wrote it here should have worked and does work for other programs which is why I mentioned this program specifically because it is giving me so much trouble.

I believe what I wrote redirects all the program output including errors into one file or one variable and indeed it does work as expected when put into a file but not when put into a variable. Also another & must be added to the end of the line to try to echo the variable or else the script will hang. But the echo as stated before shows no output.

This is important as the script is time sensitive and I have reason to believe that significant latency is being added by having to read and write to a file versus working with the data in memory which is why I would like to use a variable instead.

I have simplified the example commands above.

Essentially the problem is that redirection works but command substitution does not.

This appears to be the problem.
See this link here: https://forums.debian.net/viewtopic.php?t=52361

All I wanted to do was improve this little script I made - I figured it would take 30 minutes - and I am 12 hours in and talking about asyncronous command substitutions.

Depends on your actual code.

Attached Files

xtest.txt (108.8 KB, 6 views)

The link I posted had a hint to the bash coproc directive and that is what I used. Not before reading some condescending stuff about how coproc is useless compared to the complicated file descriptor stuff. It is remarkable that people that do this stuff from day to day would not have an open mind about when it should be used.

This fixes it.
Setup the coproc by running the program in the background:
Read the coproc any time you need to and will read all lines with '' but may not terminate until the 1 second delay specified:
Actually display the results if you want:

That should work if not backgrounded. I needed to background xinput test-xi2 so the script would continue. Thus the coproc solution.

I have never needed to background a command substitution and pull information from it so the idea that it would not work and need to be replaced with something else was new to me and required me to spend a huge amount of time figuring out what was wrong.

I do think it is important for people to see the "easy way" that you have posted so new users do not get the impression that scripting is always this hard.

Sorry, the background part was not obvious at least for me...