bash while ctrl-c inconsistent behaviour

doru · 06-19-2019, 03:03 AM

For the first while, ctrl-c breaks the loop, for the second it doesn't, it just stops arecord. Why?

Code:

while true; do sleep 1h; done
while true; do arecord somefile.wav; done

GazL · 06-19-2019, 03:59 AM

Most likely arecord is setting up its own signal handler for SIGINT, while sleep doesn't.

doru · 06-19-2019, 07:08 AM

Quote:

Originally Posted by GazL

Most likely arecord is setting up its own signal handler for SIGINT, while sleep doesn't.

sleep alone does exit on ctrl-c, like most programs. You say that the signal is passed to while?!

GazL · 06-19-2019, 02:26 PM

I don't understand the exact mechanics -- possibly it checks the return code from the sleep (code 130 when interrupted by SIGINT) -- but however it works, an interrupted command will also terminate the while loop it is contained in.

My guess is that arecord traps the SIGINT itself, and then exits normally, thus the shell/while-loop doesn't notice that it's been interrupted and starts the next iteration of the loop.

doru · 07-01-2019, 05:23 AM

Code:

$ while true; do echo a; sleep 1; false; done #does not stop at false 
$ cat while.sh #does not stop at myfunc 
myfunc() { echo b; return 130; }
while true; do
  echo a
  myfunc
  echo myfunc returns $?
  sleep 1
  done

They are definitely hiding something from us ...