slack-notify

#!/usr/bin/env bash
#
# slack-notify - send a message to a Slack Incoming Webhook
#
# Setup:
#   1. Save your webhook URL somewhere it won't be committed to git, e.g.:
#        echo 'https://hooks.slack.com/services/XXX/YYY/ZZZ' > ~/.config/slack-webhook-url
#      chmod 600 ~/.config/slack-webhook-url
#   OR
#   2. Export it as an env var in your shell profile:
#        export SLACK_WEBHOOK_URL="https://hooks.slack.com/services/XXX/YYY/ZZZ"
#
# Usage:
#   slack-notify "Server X is down"
#   echo "some log line" | slack-notify
#   slack-notify -c '#ff0000' "Disk usage critical"   # colored side-bar (attachment)

set -euo pipefail

CONFIG_FILE="${SLACK_WEBHOOK_CONFIG:-$HOME/.config/slack-webhook-url}"
COLOR=""

usage() {
  echo "Usage: $(basename "$0") [-c '#RRGGBB'] \"message\"" >&2
  echo "       echo \"message\" | $(basename "$0")" >&2
  exit 1
}

# Parse optional color flag
while getopts ":c:" opt; do
  case "$opt" in
    c) COLOR="$OPTARG" ;;
    *) usage ;;
  esac
done
shift $((OPTIND - 1))

# Resolve webhook URL: env var takes precedence, then config file
if [[ -n "${SLACK_WEBHOOK_URL:-}" ]]; then
  WEBHOOK_URL="$SLACK_WEBHOOK_URL"
elif [[ -f "$CONFIG_FILE" ]]; then
  WEBHOOK_URL="$(<"$CONFIG_FILE")"
else
  echo "Error: no webhook URL found." >&2
  echo "Set \$SLACK_WEBHOOK_URL or create $CONFIG_FILE" >&2
  exit 1
fi

# Get message from argument or stdin
if [[ $# -gt 0 ]]; then
  MESSAGE="$*"
elif ! [[ -t 0 ]]; then
  MESSAGE="$(cat)"
else
  usage
fi

if [[ -z "$MESSAGE" ]]; then
  echo "Error: empty message" >&2
  exit 1
fi

# Build JSON payload safely (works without jq via python3, falls back to naive escaping)
build_payload() {
  if command -v python3 >/dev/null 2>&1; then
    python3 - "$MESSAGE" "$COLOR" <<'PY'
import json, sys
message, color = sys.argv[1], sys.argv[2]
if color:
    payload = {"attachments": [{"color": color, "text": message}]}
else:
    payload = {"text": message}
print(json.dumps(payload))
PY
  else
    # naive fallback: escape backslashes and double quotes
    escaped="${MESSAGE//\\/\\\\}"
    escaped="${escaped//\"/\\\"}"
    printf '{"text":"%s"}' "$escaped"
  fi
}

PAYLOAD="$(build_payload)"

RESPONSE="$(curl -sS -X POST -H 'Content-type: application/json' \
  --data "$PAYLOAD" "$WEBHOOK_URL")"

if [[ "$RESPONSE" != "ok" ]]; then
  echo "Slack responded unexpectedly: $RESPONSE" >&2
  exit 1
fi