Environment & Platform¶

Configure environment variables, working directories, shells, and platform-specific behavior.

Environment variables¶

Set environment variables for a command:

serve {
    env PORT="3000" RUST_LOG="debug"
    run "cargo run --bin server"
}

Variables are set in the child process environment — they don't affect your shell.

Env files¶

Load variables from a .env file:

serve {
    env-file ".env.local"
    run "cargo run --bin server"
}

Supports standard .env syntax: comments, blank lines, quoted values, export prefix.

If both env and env-file are specified, explicit env values override env-file values:

serve {
    env-file ".env"
    env PORT="9999"    // overrides PORT from .env
    run "cargo run"
}

Working directory¶

Run a command from a different directory:

frontend {
    dir "packages/web"
    run "npm run dev"
}

The path is relative to the lets.kdl file location.

Shell override¶

By default, commands run via sh -c. Override per-command:

script {
    shell "bash"
    run "echo $BASH_VERSION"
}

Or set a default shell for all commands in config:

config {
    shell "zsh"
}

// All commands now use zsh unless they specify their own shell
build "cargo build"

Per-command shell overrides the global default.

Platform guards¶

Restrict a command to specific platforms:

install {
    platform "macos" "linux"
    run "echo installing"
}

Valid platforms: "macos", "linux", "windows". Unrecognized platform names produce a parse error.

Platform-specific run commands¶

Provide different commands for different operating systems:

install {
    description "Install dependencies"
    run-macos "brew install libpq"
    run-linux "sudo apt-get install -y libpq-dev"
    run-windows "choco install libpq"
}

Platform-specific run-* commands take priority. If the current platform has no specific variant, the generic run is used as a fallback:

install {
    run "echo unsupported platform"
    run-macos "brew install libpq"
    run-linux "apt-get install libpq-dev"
}

On macOS this runs brew install libpq. On Windows (no run-windows), it falls back to echo unsupported platform.

Global config¶

The top-level config block sets defaults for all commands:

config {
    sorted       // Sort commands alphabetically in help
    shell "zsh"  // Default shell for all commands
}