Dynamically run build commands

In this example, you'll create a vercel.sh file in your repository that your project's Build Command can use to run conditional logic..

1. Set up your scripts in package.json. Specify the following example scripts to be run for your preview and production environments:
   package.json

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   {
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     "scripts": {
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       "build:production": "next build",
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       "build:preview": "echo \"Let's build a preview!\" && next build"
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     }
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   }

2. Create a vercel.sh file in your project's root directory. Use the following conditional logic to run a script according to the environment:
   vercel.sh

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   #!/bin/bash
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   if [[ $VERCEL_ENV == "production"  ]] ; then
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     npm run build:production
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   else
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     npm run build:preview
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   fi

   You can adjust this to use any other System Environment Variables on Vercel. For example, you can use VERCEL_BRANCH_URL to run a script according to the branch name.
3. Set your Build Command to use vercel.sh either in your vercel.json file or in the project dashboard:

• Using a vercel.json file:
  vercel.json

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  {
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    "$schema": "https://openapi.vercel.sh/vercel.json",
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    "buildCommand": "sh vercel.sh"
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  }

• Using the project dashboard: Select your project from the dashboard and go to the Settings tab. Under Build & Development Settings, set the value of the Build Command to be sh vercel.sh. This runs the vercel.sh script created earlier.