Adding documentation for Codespaces default env variables (#23917)

* Adding documentation for Codespaces default env variables

* Update content/codespaces/developing-in-codespaces/default-environment-variables.md

* Update content/codespaces/developing-in-codespaces/default-environment-variables.md

* Fixing linting errors

* Update content/codespaces/developing-in-codespaces/default-environment-variables.md

Co-authored-by: Mike McDonald <2575327+asciimike@users.noreply.github.com>

* Update content/codespaces/developing-in-codespaces/default-environment-variables.md

Co-authored-by: Mike McDonald <2575327+asciimike@users.noreply.github.com>

* Update content/codespaces/developing-in-codespaces/default-environment-variables.md

Co-authored-by: Mike McDonald <2575327+asciimike@users.noreply.github.com>

* Update content/codespaces/developing-in-codespaces/default-environment-variables.md

Co-authored-by: Mike McDonald <2575327+asciimike@users.noreply.github.com>

* Update content/codespaces/developing-in-codespaces/default-environment-variables.md

Co-authored-by: Mike McDonald <2575327+asciimike@users.noreply.github.com>

* Change the title

* Change file name

and small editorial changes.

Co-authored-by: Mike McDonald <2575327+asciimike@users.noreply.github.com>
Co-authored-by: hubwriter <hubwriter@github.com>

Author: 3 people

content/codespaces/developing-in-codespaces/default-environment-variables-for-your-codespace.md

@@ -0,0 +1,40 @@
+---
+title: Default environment variables for your codespace
+shortTitle: Default environment variables
+product: '{% data reusables.gated-features.codespaces %}'
+permissions: '{% data reusables.codespaces.availability %}'
+intro: '{% data variables.product.prodname_dotcom %} sets default environment variables for each codespace.'
+versions:
+  fpt: '*'
+  ghec: '*'
+type: overview
+topics:
+  - Codespaces
+  - Fundamentals
+  - Developer
+---
+
+## About default environment variables
+
+{% data variables.product.prodname_dotcom %} sets default environment variables for every codespace. Commands run in codespaces can create, read, and modify environment variables.
+
+{% note %}
+
+**Note**: Environment variables are case-sensitive.
+
+{% endnote %}
+
+## List of default environment variables
+
+| Environment variable | Description |
+| ---------------------|------------ |
+| `CODESPACE_NAME` | The name of the codespace For example, `monalisa-github-hello-world-2f2fsdf2e` |
+| `CODESPACES` | Always `true` while in a codespace |
+| `GIT_COMMITTER_EMAIL` | The email for the "author" field of future `git` commits. |
+| `GIT_COMMITTER_NAME` | The name for the "committer" field of future `git` commits. |
+| `GITHUB_API_URL` | Returns the API URL. For example, `{% data variables.product.api_url_code %}`. |
+| `GITHUB_GRAPHQL_URL` | Returns the GraphQL API URL. For example, `{% data variables.product.graphql_url_code %}`. |
+| `GITHUB_REPOSITORY` | The owner and repository name. For example, `octocat/Hello-World`. |
+| `GITHUB_SERVER_URL`| Returns the URL of the {% data variables.product.product_name %} server. For example, `https://{% data variables.product.product_url %}`. |
+| `GITHUB_TOKEN` | A signed auth token representing the user in the codespace. You can use this to make authenticated calls to the GitHub API. For more information, see "[Authentication](/codespaces/codespaces-reference/security-in-codespaces#authentication)."  |
+| `GITHUB_USER` | The name of the user that initiated the codespace. For example, `octocat`. |

content/codespaces/developing-in-codespaces/index.md

@@ -15,6 +15,7 @@ children:
   - /using-codespaces-for-pull-requests
   - /deleting-a-codespace
   - /forwarding-ports-in-your-codespace
+  - /default-environment-variables-for-your-codespace
   - /connecting-to-a-private-network
   - /using-codespaces-in-visual-studio-code
   - /using-codespaces-with-github-cli