Bashscripts.org

Hi to everybody!
I want to repeat an action (playing an audio file) until I press a key on my keyboard.
The latter can be achieved with read -n 1, but how do I insert the whole into a loop that waits for my input and plays in the meanwhile?
I hope I've been clear enough...

Thanks in advance!

Trap might do the trick. But I believe it only handles sig's.
http://linux.die.net/man/1/trap


Another solution could be something like this.


This will run the program, and then wait for your input into read, the $tmp variable is not of any concern since you just want to use read to "pause" the script.
kill $pid will kill all the instances with the same name, so this can be a bit risky if your application is named the same way as something you really want to keep.

Best regards
Fredrik Eriksson

Thanks for your reply.

A solution for not killing all the instances with the same name may be to call pidof with -s, that returns only the last one.

Anyway, perhaps I didn't explain very well that I'd like to start looping a ring bell that plays until I press a key. Basically, I would need to break a the execution of a block of code when any input from the keyboard is received. I don't know if it's possible within a bash script...

I took a rapid look to trap, but I could not find it very useful for my purposes. A dirty trick should be:

This way I would avoid pressing Ctrl+c 2 times, one to kill aplay and one to exit the loop.

Another partial solution is:

It plays the file and then waits for the user input. If no key is pressed within 1 second, sound file is played again, otherwise the loop breaks. The drawback is that I can only stop the loop whithin the short time of a second.

Regards

Well you could always do a little if check.



Not sure if this would work, since just pressing enter would make the $tmp_var contain "" which I think is the same as zero valued variable.

Problem with using read is that there is no way of checking if the variable is set in the first place. tmp_var="" is the same as not setting tmp_var, in contrast to other programming languages where setting "" inits the variable.
PHP or perl for example can check if the variable is set by using
PERL: if($var) { }
PHP: if(isset($var)) { }

Even thou both of these languages can declare content in a variable without first typecasting or defining the existance of a variable.

If anyone have a suggestion on how to check for a variables existance I would love to hear it

Anyway, back on topic.
script1.sh


This could probably work as you want, but it's not fool proof... ctrl, alt and special keys that doesn't output a specific character won't be catched.

The best solution might be to either find a perl extension library which is built to handle keypresses or write a program in c or the like which can exit with a return value.

Anyway, going to stop ranting now and get back to work

Best regards
Fredrik Eriksson

The temp file approach seems the best so far and it was my next option indeed.

It's not fool proof too, but it does the trick!
Thanks for your help.

this only returns non-empty if myvar is set


Also the following can be useful, causes bash to error when it tries to expand an unset variable