Vercel has added a System Variable for the pull request number. This package is now deprecated.

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vercel-is-pull-request

CLI which adds pull request environment variables to Vercel builds.

It adds the following variables:

Name	Description
VERCEL_GIT_IS_PULL_REQUEST	An indicator that the current build has a corresponding pull request. Example: 1.
VERCEL_GIT_PULL_REQUEST_NUMBER	The pull request number the build corresponds to. Example: 36. This is only set if VERCEL_GIT_IS_PULL_REQUEST is 1.

Usage

To use this, first install it as a dependency.

npm install vercel-is-pull-request

Then, update your build command to include the following command:

source node_modules/.bin/vercel-is-pull-request

If you are building a private GitHub repository add a access token through the --auth argument like so:

source node_modules/.bin/vercel-is-pull-request --auth githubaccesstoken

Now inside your build step you can access the added environment variables to change the build.

if (process.env.VERCEL_GIT_IS_PULL_REQUEST === '1') {
  console.log(`Building preview of pull request: https://github.com/useparcel/vercel-is-pull-request/pulls/${process.env.VERCEL_GIT_PULL_REQUEST_NUMBER}`)
}