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How to create a Git commit (the hard way!) with the GitHub API

This is a walkthrough for how to make a Git commit the hard way using the GitHub API, testing the steps with cURL via the command line. The easy way: If you just want to update or create a single file, you can do it the easy way following the API docs here: https://developer.github.com/v3/repos/contents/

Prerequisites

Setup

  • Make sure you have cURL installed; we'll be using it to make GET and POST requests to GitHub's API via the command line.
  • Create a GitHub personal access token and choose the repo scope to make sure you have the permissions required to access your GitHub repositories through the API. Save the generated access token somewhere safe, and treat it like a password! Don't share it with anyone or publish it anywhere!
  • When running the code snippets below, replace TOKEN-GOES-HERE with your new personal access token.

Sources

1. Get the SHA of the previous commit

API Docs: https://developer.github.com/v3/git/refs/#get-a-reference

To access the latest commit, get a reference to the HEAD of the desired branch by making a GET request to /repos/:user/:repo/git/refs/heads/:branch. For example:

curl -i -H 'Authorization: token TOKEN-GOES-HERE' https://api.github.com/repos/LearnTeachCode/git-notes/git/refs/heads/master

GitHub will send a response containing some JSON data for the requested commit. Here's the important bit:

"object": {
    "sha": "d176c1442aa83adfbcf9746464fd4733bf1106d6",
    "type": "commit",
    "url": "https://api.github.com/repos/LearnTeachCode/git-notes/git/commits/d176c1442aa83adfbcf9746464fd4733bf1106d6"
  }

Save the SHA, because we'll need it for the next steps!

2. Get the tree of the previous commit

API Docs: https://developer.github.com/v3/git/trees/#get-a-tree

Using the SHA saved from Step 1, make a GET request to /repos/:owner/:repo/git/trees/:sha. For example:

curl -i -H 'Authorization: token TOKEN-GOES-HERE' https://api.github.com/repos/LearnTeachCode/git-notes/git/commits/d176c1442aa83adfbcf9746464fd4733bf1106d6

GitHub will send a response with the data for the requested tree. (In Git, trees represent the hierarchy of files and folders. A tree contains references to files, called blobs, or sub-folders, called trees.) Looking at the response, here's the important part:

"tree": {
    "sha": "60eeced8d029c08d6ef8c3ac5ee806ac048b2aba",
    "url": "https://api.github.com/repos/LearnTeachCode/git-notes/git/trees/60eeced8d029c08d6ef8c3ac5ee806ac048b2aba"
  }

Save the SHA of this tree, because we'll need it for the next steps!

3. Create a new blob (file)

API Docs: https://developer.github.com/v3/git/blobs/#create-a-blob

In Git, files are stored in objects called blobs. Create a new blob by making a POST request to /repos/:user/:repo/git/blobs with a payload like this: {"content": "# This is a test!", "encoding": "utf-8"}.

curl -i -H 'Authorization: token TOKEN-GOES-HERE' https://api.github.com/repos/LearnTeachCode/git-notes/git/blobs -d '{"content": "# This is a test!", "encoding": "utf-8"}'

After creating the new blob, GitHub's response will look like this:

{
  "sha": "6d24476b2db867038f550c22b68c664cd34d89b1",
  "url": "https://api.github.com/repos/LearnTeachCode/git-notes/git/blobs/6d24476b2db867038f550c22b68c664cd34d89b1"
}

Save the SHA of the new blob, because we'll need it for the next steps!

4. Create new tree

API Docs: https://developer.github.com/v3/git/trees/#create-a-tree

When creating a new tree, we need to specify the base tree to link it to and the contents of the new tree -- in this case, just a single file (the blob we created in Step 3), which we'll name test.md. Create a new tree by creating a POST request to /repos/:user/:repo/git/trees/ with the following payload: {"base_tree": "SHA-FROM-STEP2-GOES-HERE", "tree": [{"path": "test.md", "mode": "100644", "type": "blob", "sha": "SHA-FROM-STEP3-GOES-HERE"}]}.

curl -i -H 'Authorization: token TOKEN-GOES-HERE' https://api.github.com/repos/LearnTeachCode/git-notes/git/trees -d '{"base_tree": "60eeced8d029c08d6ef8c3ac5ee806ac048b2aba", "tree": [{"path": "test.md", "mode": "100644", "type": "blob", "sha": "6d24476b2db867038f550c22b68c664cd34d89b1"}]"}'

After creating the new tree, GitHub's response will show the contents of the new tree, along with the SHA and URL for our newly-created tree:

{
  "sha": "13f7216098033199493d9bc08b141922d3d46985",
  "url": "https://api.github.com/repos/LearnTeachCode/git-notes/git/trees216098033199493d9bc08b141922d3d46985",
  "tree": [
      // ...TREE DATA HERE...
  ],
  "truncated": false
}

Save the SHA of the new tree, because -- you guessed it! -- we'll need this for the next step!

5. Make the commit

API Docs: https://developer.github.com/v3/git/commits/#create-a-commit

Now we can finally make a commit! To create the new commit, make a POST request to /repos/:user/:repo/git/commits with the payload {"parents": ["SHA-FROM-STEP1-GOES-HERE"], "tree": "SHA-FROM-STEP4-GOES-HERE", "message": "Testing remote commit via GitHub API"}.

curl -i -H 'Authorization: token TOKEN-GOES-HERE' https://api.github.com/repos/LearnTeachCode/git-notes/git/commits -d '{"parents": ["d176c1442aa83adfbcf9746464fd4733bf1106d6"], "tree": "13f7216098033199493d9bc08b141922d3d46985", "message": "Testing remote commit via GitHub API"}'

After creating the new commit, GitHub's response will show data about the commit and its author (you!), but the only piece we need is the SHA:

{
 "sha": "59fd06d961f2d65423aaab59139babcb4413486f",
 "url": "https://api.github.com/repos/LearnTeachCode/git-notes/git/commits/59fd06d961f2d65423aaab59139babcb4413486f",
 "html_url": "https://github.com/LearnTeachCode/git-notes/commit/59fd06d961f2d65423aaab59139babcb4413486f",  
 // ...OTHER DATA HERE...
}

So once again, save the SHA of the newly-created commit, because we'll need it for our last step!

6. Move the commit to the branch

API Docs: https://developer.github.com/v3/git/refs/#update-a-reference

For our last step, we'll update the HEAD reference, pointing it to the new commit by making a PATCH or POST request to /repos/:user/:repo/git/refs/heads/:branch with the payload {"sha": "SHA-FROM-STEP5-GOES-HERE"}. In this case, we're updating the master branch:

curl -i -H 'Authorization: token TOKEN-GOES-HERE' https://api.github.com/repos/LearnTeachCode/git-notes/git/refs/heads/master -d '{"sha": "59fd06d961f2d65423aaab59139babcb4413486f"}'

Congrats! To check that it worked as expected, take a look at the GitHub project page. A new file named test.md should now be listed with the rest of the files, and the latest commit should reflect the changes!