Simple email sending with sendgrid

mail.sh

#!/bin/bash

if [ -z "$SENDGRID_API_KEY" ] ; then
    echo "No Sendgrid api key specified. export SENDGRID_API_KEY=..."
    exit 1
fi

subject=""
from="$USER@$(hostname)"

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

shift $((OPTIND - 1))
body="$(cat)"
if [ -z "$subject" ] ; then
    subject="-"
fi

jq -n --arg to "$*" \
      --arg subject "$subject" \
      --arg from "$from" \
      --arg body "$body" \
'{
  "personalizations": [
    {
      "to": $to | split(" ") | map({"email": .}),
      "subject": $subject
    }
  ],
  "from": {
    "email": $from
  },
  "content": [
    {
      "type": "text/plain",
      "value": $body
    }
  ]
}' | \
    curl -sX POST https://api.sendgrid.com/v3/mail/send \
     -H "Authorization: Bearer $SENDGRID_API_KEY" \
     -H "Content-Type: application/json" \
     -d @-