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I am using Ubuntu 12.04.2. I am trying to use "trap" command to capture abnormal or error in my shell script but I am also trying to manually trigger "Error" exit.

I have tried exit 1, but it won't trigger "Error" signal.


    exit 1

trap "echo hi" INT TERM ERR

Not sure how to manually trigger "Error" exit signal?

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1 Answer 1

up vote 6 down vote accepted

the ERR trap is not to run code when the shell itself exits with a non-zero error code, but when any command run by that shell that is not part of a condition (like in if cmd..., or cmd || ......) exits with a non-zero exit status (the same conditions as what causes set -e to exit the shell).

If you want to run code upon exit of the shell with non-zero exit status, you should add a trap on EXIT instead and check $? there:

trap '[ "$?" -eq 0 ] || echo hi' EXIT

Note however that upon a trapped signal, both the signal trap and the EXIT trap would be run, so you may want to do it like:

trap killed_by=INT INT
trap killed_by=TERM TERM
trap '
  if [ -n "$killed_by" ]; then
    echo >&2 "Ouch! Killed by $killed_by"
    exit 1
  elif [ "$ret" -ne 0 ]; then
    echo >&2 "Died with error code $ret"
  fi' EXIT

Or to use exit status like $((signum + 128)) upon signals:

for sig in INT TERM HUP; do
  trap "exit $((128 + $(kill -l "$sig")))" "$sig"
trap '
  [ "$ret" -eq 0 ] || echo >&2 "Bye: $ret"' EXIT

If you want the ERR trap to fire, just run a command with a non-zero exit status like false or test.

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