commands.sh

$ git log --since=2018-01-01 --pretty='%H %ae' | awk '{ users[$2] = $1 } END { for (u in users) { print users[u] } }' | sed -E 's/^(.+)$/object(oid: "\1") { ...author }/'
# c_9678fb4f85eeb6fd91a89caa255d7a80131a6fc5: object(oid: "9678fb4f85eeb6fd91a89caa255d7a80131a6fc5") { ...author }

curl -H "Authorization: token xxx" 'https://api.github.com/graphql' -X POST -d "{\"query\":\"$(sed 's/"/\\\\\\"/g' users.graphql | xargs echo)\"}" > output.json

output.json

{
  "data": {
    "repository": {
      "c_9678fb4f85eeb6fd91a89caa255d7a80131a6fc5": {
        "author": {
          "user": {
            "login": "someone"
          }
        }
      },
      ...
    }
  }
}

users.graphql

query {
  repository(owner: "Shopify", name: "shopify") {
    c_9678fb4f85eeb6fd91a89caa255d7a80131a6fc5: object(oid: "9678fb4f85eeb6fd91a89caa255d7a80131a6fc5") { ...author }
    c_a35c31bd37d16b1ecb54d5d7a534616d3bb8d7d8: object(oid: "a35c31bd37d16b1ecb54d5d7a534616d3bb8d7d8") { ...author }
    ...
  }
}

fragment author on GitObject {
  ... on Commit {
    author {
      user {
        login
      }
    }
  }
}