cross-env

cross-env is a utility that allows you to set environment variables inline in npm scripts in a way that works across Windows, macOS, and Linux. On Unix-like systems, setting environment variables inline is straightforward (NODE_ENV=production node app.js), but Windows Command Prompt and PowerShell use different syntax (set NODE_ENV=production), creating cross-platform compatibility issues in package.json scripts. cross-env normalizes this by providing a command wrapper: cross-env NODE_ENV=production node app.js works identically on all platforms. The tool parses the command line, sets the specified environment variables using Node.js's child_process.spawn, and executes the remaining command in a child process. cross-env supports multiple environment variables, quoted values containing spaces, and variable expansion. The cross-env-shell variant uses shell execution for commands that need shell features like piping and globbing. While newer approaches like dotenv or Node.js's --env-file flag reduce the need for inline environment variables, cross-env remains essential for npm scripts that need to work across development environments with different operating systems. It is one of the most widely used cross-platform utilities in the npm ecosystem.