webhook-notify.sh

#!/usr/bin/env bash

set -o errexit
set -o nounset
set -o pipefail

log() {
    echo >&2 "$*"
}

usage() {
    set +o xtrace
    log "Usage: webhook-notify [-u=<url>] [-v] [-h] [--] (<text>...|-)
Message contents will be read from arguments or stdin.
Options:
  -u    Webhook url
  -v    Verbose output
  -h    Print help
Supported Webhook providers:
  Google Chat ( https://chat.googleapis.com/v1/spaces/... )
  Discord     ( https://discord.com/api/webhooks/... )
Config:
  The program will attempt to read a config file from: /etc/webhook-notify.cfg
  The config may contain the target webhook url like this:
    url=\"<webhook_url>\"
Mail:
  To redirect incoming mail to discord, configure /etc/aliases like this:
    discord: \"|/usr/local/bin/webhook-notify\"
    root: discord
"
}

check_dependency() {
    if ! command -v "$1" > /dev/null 2>&1; then
        log "Error: missing dependency: $1"
        exit 1
    fi
}

read_stdin() {
    if [[ -p /dev/stdin ]]; then
        local line
        while IFS= read -r line; do
            echo "${line}"
        done
    fi
}

check_dependency curl
check_dependency jq

cfg="/etc/webhook-notify.cfg"
if [[ -r "${cfg}" ]]; then
    source "${cfg}"
fi

while getopts u:vh opt; do
    case $opt in
        u) url="$OPTARG" ;;
        v) set -o xtrace ;;
        h) usage ; exit 0 ;;
        *) usage ; exit 1 ;;
    esac
done
shift $((OPTIND - 1))

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

set +o nounset

if [[ -z $url ]]; then
    log "Error: webhook url required"
    usage ; exit 1
fi

if [[ -z $text ]]; then
    log "Error: missing message content"
    usage ; exit 1
fi

set -o nounset

if echo "${url}" | grep --quiet --extended-regexp "https\:\/\/chat.googleapis\.com\/v1\/.*"; then
    payload="$(echo '{"text": ""}' | jq --raw-output --arg text "$text" '.text |= $text')"
elif echo "${url}" | grep --quiet --extended-regexp "https\:\/\/discord\.com\/api\/webhooks\/.*"; then
    payload="$(echo '{"content": ""}' | jq --raw-output --arg text "$text" '.content |= $text')"
else
    log "Error: unknown webhook provider"
    exit 1
fi

curl \
    --request POST \
    --header "Content-Type: application/json; charset=UTF-8" \
    --data "${payload}" \
    "$url"