Shell logging to Slack Webhook

slack_log.sh

#!/bin/bash

#######################################
# Send log message to Slack channel via Webhook.
#
# @author Yuriy Belenko <yura-bely@mail.ru>
# This functions requires jo package installed. https://github.com/jpmens/jo
#
# Originally developed as almost zero dependency(jo only) alternative of Slack Monolog PHP handler:
# https://github.com/Seldaek/monolog/blob/main/src/Monolog/Handler/SlackWebhookHandler.php
#
# Ref to Slack webhook doc: https://api.slack.com/messaging/webhooks
# Globals:
#   SLACK_WEBHOOK
# Arguments:
#   $1 message
#   $2 (optional) log level, eg DEBUG or code equivalent 100
# Returns:
#   nothing if message has been sent, non-zero on error.
#######################################
function slack_log() {
  local level='DEBUG' color='#e3e4e6' payload attachment log_level_field timestamp
  timestamp=$(date +%s)

  if [[ -z "${SLACK_WEBHOOK}" ]]; then
    echo "Error: SLACK_WEBHOOK constant required for slack_log" >&2
    return 1
  fi

  if [[ -z "$1" ]]; then
    echo 'Error: at least one argument requred in slack_log()' >&2
    return 1
  fi

  if [[ -n "$2" ]]; then
    # log level specified
    case "$2" in
    DEBUG | 100)
      level='DEBUG'
      color='#e3e4e6'
      ;;
    INFO | 200)
      level='INFO'
      color='good'
      ;;
    NOTICE | 250)
      level='NOTICE'
      color='good'
      ;;
    WARNING | 300)
      level='WARNING'
      color='warning'
      ;;
    ERROR | 400)
      level='ERROR'
      color='danger'
      ;;
    CRITICAL | 500)
      level='CRITICAL'
      color='danger'
      ;;
    ALERT | 550)
      level='ALERT'
      color='danger'
      ;;
    EMERGENCY | 600)
      level='EMERGENCY'
      color='danger'
      ;;
    *)
      echo 'Error: Invalid log level in slack_log()' >&2
      return 1
      ;;
    esac
  fi

  log_level_field=$(jo title="Level" value="${level}" short@0)
  attachment=$(jo title="Message" fallback="$1" text="$1" color="${color}" fields[]="${log_level_field}" mrkdwn_in="fields" ts="${timestamp}")
  payload=$(jo attachments[]="${attachment}")

  curl --request POST \
    --url "${SLACK_WEBHOOK}" \
    --header 'Content-type: application/json' \
    --data "${payload}"
}