Slack Webhook Shell Script Linux

Slack webhook shell scripts are the fastest way to get cron and backup jobs out of email silos — one curl POST with JSON {"text": "..."} and your channel sees failures in real time.

What this script does

Accepts message as arguments or stdin
Builds JSON safely with Python one-liner (no broken escapes)
Configurable WEBHOOK_URL env var
Optional username and emoji for bot appearance
Non-zero curl exit fails the script for cron wrappers

Prerequisites

curl and python3
Slack incoming webhook URL from app settings
Outbound HTTPS

Step 1: Save the script

sudo nano /usr/local/bin/slack-notify.sh
sudo chmod +x /usr/local/bin/slack-notify.sh

Step 2: Full script (scroll to read)

slack-notify.sh

#!/usr/bin/env bash
set -euo pipefail

WEBHOOK_URL="${WEBHOOK_URL:?set WEBHOOK_URL to Slack incoming webhook}"
USER_NAME="${SLACK_USER:-server-bot}"
EMOJI="${SLACK_EMOJI:-:computer:}"

if [[ $# -gt 0 ]]; then
  text="$*"
else
  text="$(cat)"
fi

payload=$(TEXT="$text" USER_NAME="$USER_NAME" EMOJI="$EMOJI" python3 -c 'import json,os; print(json.dumps({"text":os.environ["TEXT"],"username":os.environ.get("USER_NAME","server-bot"),"icon_emoji":os.environ.get("EMOJI",":computer:")}))')

curl -fsS -X POST -H 'Content-type: application/json' --data "$payload" "$WEBHOOK_URL"
echo

Scroll inside the box to read the full script.

Step 3: Configure settings

Store webhook in /etc/slack-webhook.env mode 600 — source from scripts
Combine with log error alert scripts on this blog
Do not log full webhook URL in world-readable files

Shell script posting to Slack incoming webhook

Step 4: Test manually

WEBHOOK_URL='https://hooks.slack.com/services/XXX' ./slack-notify.sh 'Test from server'

echo exit=$?

Schedule with cron

sudo crontab -e

Add:

# at end of backup: /usr/local/bin/slack-notify.sh 'MySQL backup OK on $(hostname -s)'

Slack Webhook Notification Shell Script (curl JSON from Linux Cron)