log.sh

#!/bin/bash

set -uo pipefail;

function _log_exception() {
  (
    BASHLOG_FILE=0;
    BASHLOG_JSON=0;
    BASHLOG_SYSLOG=0;

    log 'error' "Logging Exception: ${@}";
  );
}

function log() {
  local date_format="${BASHLOG_DATE_FORMAT:-+%F %T}";
  local date="$(date "${date_format}")";
  local date_s="$(date "+%s")";

  local file="${BASHLOG_FILE:-0}";
  local file_path="${BASHLOG_FILE_PATH:-/tmp/$(basename "${0}").log}";

  local json="${BASHLOG_JSON:-0}";
  local json_path="${BASHLOG_JSON_PATH:-/tmp/$(basename "${0}").log.json}";

  local syslog="${BASHLOG_SYSLOG:-0}";
  local tag="${BASHLOG_SYSLOG_TAG:-$(basename "${0}")}";
  local facility="${BASHLOG_SYSLOG_FACILITY:-local0}";
  local pid="${$}";

  local level="${1}";
  local upper="$(echo "${level}" | awk '{print toupper($0)}')";
  local debug_level="${DEBUG:-0}";

  shift 1;

  local line="${@}";

  # RFC 5424
  #
  # Numerical         Severity
  #   Code
  #
  #    0       Emergency: system is unusable
  #    1       Alert: action must be taken immediately
  #    2       Critical: critical conditions
  #    3       Error: error conditions
  #    4       Warning: warning conditions
  #    5       Notice: normal but significant condition
  #    6       Informational: informational messages
  #    7       Debug: debug-level messages

  local -A severities;
  severities['DEBUG']=7;
  severities['INFO']=6;
  severities['NOTICE']=5; # Unused
  severities['WARN']=4;
  severities['ERROR']=3;
  severities['CRIT']=2;   # Unused
  severities['ALERT']=1;  # Unused
  severities['EMERG']=0;  # Unused

  local severity="${severities[${upper}]:-3}"

  if [ "${debug_level}" -gt 0 ] || [ "${severity}" -lt 7 ]; then

    if [ "${syslog}" -eq 1 ]; then
      local syslog_line="${upper}: ${line}";

      logger \
        --id="${pid}" \
        -t "${tag}" \
        -p "${facility}.${severity}" \
        "${syslog_line}" \
        || _log_exception "logger --id=\"${pid}\" -t \"${tag}\" -p \"${facility}.${severity}\" \"${syslog_line}\"";
    fi;

    if [ "${file}" -eq 1 ]; then
      local file_line="${date} [${upper}] ${line}";
      echo -e "${file_line}" >> "${file_path}" \
        || _log_exception "echo -e \"${file_line}\" >> \"${file_path}\"";
    fi;

    if [ "${json}" -eq 1 ]; then
      local json_line="$(printf '{"timestamp":"%s","level":"%s","message":"%s"}' "${date_s}" "${level}" "${line}")";
      echo -e "${json_line}" >> "${json_path}" \
        || _log_exception "echo -e \"${json_line}\" >> \"${json_path}\"";
    fi;

  fi;

  local -A colours;
  colours['DEBUG']='\033[34m'  # Blue
  colours['INFO']='\033[32m'   # Green
  colours['NOTICE']=''         # Unused
  colours['WARN']='\033[33m'   # Yellow
  colours['ERROR']='\033[31m'  # Red
  colours['CRIT']=''           # Unused
  colours['ALERT']=''          # Unused
  colours['EMERG']=''          # Unused
  colours['DEFAULT']='\033[0m' # Default

  local norm="${colours['DEFAULT']}";
  local colour="${colours[${upper}]:-\033[31m}";

  local std_line="${colour}${date} [${upper}] ${line}${norm}";

  # Standard Output (Pretty)
  case "${level}" in
    'info'|'warn')
      echo -e "${std_line}";
      ;;
    'debug')
      if [ "${debug_level}" -gt 0 ]; then
        echo -e "${std_line}";
      fi;
      ;;
    'error')
      echo -e "${std_line}" >&2;
      if [ "${debug_level}" -gt 0 ]; then
        echo -e "Here's a shell to debug with. 'exit 0' to continue. Other exit codes will abort - parent shell will terminate.";
        bash || exit "${?}";
      fi;
      ;;
    *)
      log 'error' "Undefined log level trying to log: ${@}";
      ;;
  esac
}

declare prev_cmd="null";
declare this_cmd="null";
trap 'prev_cmd=$this_cmd; this_cmd=$BASH_COMMAND' DEBUG \
  && log debug 'DEBUG trap set' \
  || log error 'DEBUG trap failed to set';

# This is an option if you want to log every single command executed,
# but it will significantly impact script performance and unit tests will fail

#trap 'prev_cmd=$this_cmd; this_cmd=$BASH_COMMAND; log debug $this_cmd' DEBUG \
#  && log debug 'DEBUG trap set' \
#  || log error 'DEBUG trap failed to set';