logger.sh

#!/bin/bash
declare -A levels=([DEBUG]=10 [INFO]=20 [WARN]=30 [ERROR]=40)
if [[ ${levels[${__loglevel}]+isset} ]];then
  __loglevel=${levels[${__loglevel}]}
elif [[ "${__loglevel}" =~ ^[0-9]+$ ]];then
  :
else
  __loglevel=${levels['INFO']}
fi

log() {
  __level=${1:-INFO}
  while IFS= read -r line; do
    if [[ ${levels[${__level}]} < ${__loglevel} ]];then
      :
    else
      printf '%(%F %T %Z)T [%s] %s: %s\n' "-1" "$$" "${__level}" "${line}" >> ${__log:-/dev/null}
    fi
  done
}

# Setup outputs:
# 1 = LOG
# 2 = ERROR
# 3 = New STDOUT, for outputting to user
# 4 = New STDERR, for outputting to user
# 5 = DEBUG
exec 3>&1 4>&2 5> >(log DEBUG) 1> >(log) 2> >(log ERROR)