Send slack messages

slack.sh

#!/bin/bash

if [ -z "$SLACK_WEBHOOK" ] ; then
    echo "No Slack webhook specified. export SLACK_WEBHOOK=..."
    exit 1
fi

username=""

while getopts ":u:" opt; do
  case $opt in
    u)
        username="$OPTARG"
      ;;
    \?)
      echo "Invalid option: -$OPTARG" >&2
      exit 1
      ;;
    :)
      echo "Option -$OPTARG requires an argument." >&2
      exit 1
      ;;
  esac
done

shift $((OPTIND - 1))
channel="$1"
body="$(cat)"

jq -n --arg username "$username" \
      --arg body "$body" \
      --arg channel "$channel" \
'{
    "username": $username,
    "channel": $channel,
    "text": $body
}' | jq 'map_values(if . == "" then null else . end)' | \
    curl -X POST "$SLACK_WEBHOOK" \
        -H 'Content-type: application/json' \
        -d @-