Handling multiple signals with one trap in bash

Question

There is question about multiple bash traps for same signal. What about the opposite version? Is possible to write something like this:

sighand () {
  case $1 in
    1)
      echo "CATCH: SIGHUP"
      ;;
    2)
      echo "CATCH: SIGINIT"
      ;;

    ...
    # ALL EXCEPT 9
    ...

  esac
 };

 trap sighand ALL

instead of this:

sighand () {
  echo "CATCH: TERM"
};
trap sighand TERM

This is not possible we cannot determine which signal is received in shell script. For multiple signals you can have single commands but we cannot differentiate in between them. — Sriharsha Kalluru, May 11 '15 at 07:14

score 4 · Answer 1 · edited Feb 05 '20 at 08:57

You would have to write separate function for each signal:

handle_hup () {
  echo "CATCH: SIGHUP";
}
handle_int () {
  echo "CATCH: INT";
}

trap handle_hup HUP
trap handle_int INT

As a workaround you could write a custom function to set all the traps for you. Then you would call the function with all the signals you want to be handled: _trap [sig1] [sig2] ...

handle_sig () {
  case "$1" in
    HUP)
      echo "CATCH: SIGHUP"
      ;;
    INT)
      echo "CATCH: SIGINT"
      ;;
    *)
      echo "CATCH: SIG$1"
      ;;
  esac
}

_trap () {
  for sig in "$@"
  do
    trap "handle_sig $sig" "$sig"
  done
}

_trap INT HUP USR1

PhilipA · Answer 2 · 2020-04-15T22:05:24.043

This answer should do it: Identifying received signal name in Bash. I've used it for a similar reason. A minor extention to @Leistungsabfall's above. This amendment adds the ability to specify a function to use in the trap by name. Example here:

trap_with_arg() {
    func="$1" ; shift
    for sig ; do
        trap "$func $sig" "$sig"
    done
}

function handler() {
  local SIGNAL=${1}
  [ "${DEBUG}" -gt "0" ] && echo "Received Signal: ${SIGNAL}" >&2

  case "${SIGNAL}" in
    EXIT)
      [ "${DEBUG}" -gt "0" ] && echo "EXIT clause"
      # ^C
      ;;
    USR2)
      [ "${DEBUG}" -gt "0" ] && echo "DUSR2 clause"
      ;;
    HUP|USR1)
      [ "${DEBUG}" -gt "0" ] && echo "HUP|USR1 clause"
      ;;
    ABRT)
      [ "${DEBUG}" -gt "0" ] && echo "ABRT clause"
      ;;
    INT|TERM)
      [ "${DEBUG}" -gt "0" ] && echo "INT|TERM clause"
      ;;
  esac
  exit 0
}

trap_with_arg handler USR1 USR2 HUP INT ABRT TERM EXIT

Nathan SR · Answer 3 · 2021-09-29T04:12:21.027

0

Handling multiple signals with one trap in bash :

trap '' 2 3 6 15 18 20

Only Close Terminal Window will work in this case to Quit the Script.

This one liner is taken from my open source project called Automated_Quiz, which is hosted here : https://sourceforge.net/projects/automated-quiz/

Also check : https://www.computerhope.com/unix/signals.htm

edited Sep 29 '21 at 04:12

answered Sep 16 '21 at 00:53

Nathan SR

29
2

As it’s currently written, your answer is unclear. Please [edit] to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers [in the help center](/help/how-to-ask). – Community Sep 16 '21 at 04:10

Handling multiple signals with one trap in bash

3 Answers3