Code to detect "control-c" or failure in a bash script

Question

I wrote a bash script to automate a very long process. It works good.

However, if the user should control-c or rerun due to a ssh disconnect I find that there is a remnant of the previous execution still running if I: ps -ef|grep myprogram.

I believe the problem is in this snippet of code in which I background each step so I can show the user a spinning progress bar:

<snippet begin>
function progress {
 SPIN='-\|/'
 # Run the base 64 code in the background
 echo $THECOMMAND | base64 -d|bash &
 pid=$! # Process Id of the previous running command
 i=0
 while kill -0 $pid 2>/dev/null
  do
   i=$(( (i+1) %4 ))
   # Print the spinning icon so the user knows the command is running
   printf "\r$COMMAND:${SPIN:$i:1}"
   sleep .2
  done
 printf "\r"
}
<snippet end>

Question: What code can I add to my script that will detect a failure or control-c and kill the background process?

Additional info: I run the script from a wrapper and I run this in a screen session.

myprogram.sh $1 > >(tee -a /var/tmp/myprogram_install$DATE.log) 2> >(tee -a /var/tmp/myprogram_install$DATE.log >&

Look up the trap command

123
– 123

2017-11-02 15:32:56 +00:00
Commented Nov 2, 2017 at 15:32 — 123
– 123, Commented Nov 2, 2017 at 15:32

Satō Katsura · Accepted Answer · 2017-11-02 15:44:42Z

5

One way to do it:

quit=n
trap 'quit=y' INT

progress() {
 SPIN='-\|/'
 # Run the base 64 code in the background
 echo $THECOMMAND | base64 -d|bash &
 pid=$! # Process Id of the previous running command
 i=0
 while kill -0 $pid 2>/dev/null
  do
   if [ x"$quit" = xy ]; then
    kill $pid
    break
   fi
   i=$(( (i+1) %4 ))
   # Print the spinning icon so the user knows the command is running
   printf "\r$COMMAND:${SPIN:$i:1}"
   sleep .2
  done
 printf "\r"
}

answered Nov 2, 2017 at 15:44

Satō Katsura

13.7k2 gold badges34 silver badges52 bronze badges

Thanks. Pleading ignorance here. Can you help me understand how this works? I assume INT is an interrupt?? How does x"$quit" = xy get evaluated?

Marinaio
– Marinaio

2017-11-02 18:25:32 +00:00
Commented Nov 2, 2017 at 18:25
1

No. INT is the SIGINT signal, and [ x"$quit" = xy ] is the test $quit == y. When you press Ctrl-C a SIGINT signal is delivered to your script, and quit is set to y because of trap. You can then test for the value of quit in your function.

Satō Katsura
– Satō Katsura

2017-11-02 19:01:56 +00:00
Commented Nov 2, 2017 at 19:01

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