bash stacktrace

gistfile1.sh

function errexit() {
  local err=$?
  set +o xtrace
  local code="${1:-1}"
  echo "Error in ${BASH_SOURCE[1]}:${BASH_LINENO[0]}. '${BASH_COMMAND}' exited with status $err"
  # Print out the stack trace described by $function_stack  
  if [ ${#FUNCNAME[@]} -gt 2 ]
  then
    echo "Call tree:"
    for ((i=1;i<${#FUNCNAME[@]}-1;i++))
    do
      echo " $i: ${BASH_SOURCE[$i+1]}:${BASH_LINENO[$i]} ${FUNCNAME[$i]}(...)"
    done
  fi
  echo "Exiting with status ${code}"
  exit "${code}"
}

# trap ERR to provide an error handler whenever a command exits nonzero
#  this is a more verbose version of set -o errexit
trap 'errexit' ERR
# setting errtrace allows our ERR trap handler to be propagated to functions,
#  expansions and subshells
set -o errtrace

What is the purpose of line 4: local code="${1:-1}" ? It seems like $1 will never be set, so $code will always be simply 1.

@parke it's been almost a decade since I wrote this, so my memory is a little fuzzy.

I think there might have been cases where I called the error handler directly instead of through the trap in a few places, particularly if I wanted a stack trace but didn't want my script to exit.

@trainman419 I have discovered one reason you might want to receive codes via $1. Namely, so you can send multiple traps to the same handler, yet distinguish between them. For example:

trap  'errexit  ERR '  ERR
trap  'errexit  TERM'  TERM

Relatedly, you might want to do the following:

trap  'errexit   '  ERR
trap  'errexit  1'  TERM

The reason is that on ERR, $? will be non-zero. However on SIGTERM, $? will be zero. So if you want to exit with non-zero on a trap of SIGTERM, that non-zero value needs to come from somewhere other than $?.