Creating Files

The files option allows you to declaratively create configuration files and scripts in your development environment. Files are automatically generated from structured data and symlinked into your project when entering the shell.

This is particularly useful for:

• Generating configuration files from Nix data structures
• Creating executable scripts
• Setting up project-specific configurations
• Ensuring consistent file contents across the team

Supported Formats

devenv supports multiple file formats out of the box:

• json - JSON format
• ini - INI format
• yaml - YAML format
• toml - TOML format
• text - Plain text

Basic Examples

JSON Files

devenv.nix

{
  files."config.json".json = {
    database = {
      host = "localhost";
      port = 5432;
    };
    features = [ "auth" "api" "ui" ];
  };
}

This creates a config.json file:

{
  "database": {
    "host": "localhost",
    "port": 5432
  },
  "features": ["auth", "api", "ui"]
}

YAML Files

devenv.nix

{
  files."docker-compose.yml".yaml = {
    version = "3.8";
    services = {
      web = {
        image = "nginx:latest";
        ports = [ "8080:80" ];
      };
    };
  };
}

TOML Files

devenv.nix

{
  files."config.toml".toml = {
    title = "My App Config";

    server = {
      host = "0.0.0.0";
      port = 8000;
    };
  };
}

INI Files

devenv.nix

{
  files."settings.ini".ini = {
    general = {
      debug = "true";
      log_level = "info";
    };
    database = {
      connection_string = "postgres://localhost/mydb";
    };
  };
}

Text Files

For plain text files, simply provide a string:

devenv.nix

{
  files."README.txt".text = ''
    This is a development environment.
    Run `devenv shell` to get started.
  '';
}

Executable Files

You can make any file executable by setting the executable attribute:

devenv.nix

{
  files."setup.sh" = {
    text = ''
      #!/bin/bash
      echo "Running setup..."
      npm install
    '';
    executable = true;
  };
}

This is particularly useful for:

• Shell scripts that need to be executed
• Custom tooling and utilities
• Git hooks

Copying Files Instead of Symlinking

By default, files are symlinked to a read-only path in the Nix store, so they cannot be edited. Set the copyMode attribute to materialize an editable file instead:

devenv.nix

{
  # Seed an editable template once; never overwrites the user's edits.
  files.".env.local".copyMode = "seed";
  files.".env.local".text = ''
    API_URL=http://localhost:8080
  '';

  # Always overwrite with a fresh writable copy on every shell entry.
  files."config/generated.toml".copyMode = "copy";
  files."config/generated.toml".toml = {
    server.port = 8000;
  };
}

The copyMode attribute accepts:

• symlink (default): symlink to the read-only file in the Nix store. Edits are not possible; devenv keeps the link pointed at the current contents.
• seed: copy the file into place once, only if it does not already exist, and make it writable. Existing files are left untouched, so your edits are preserved. This is useful for seeding configuration files from templates that the user can then edit to fit their project.
• copy: copy the file into place as a writable file, overwriting it with fresh contents on every shell entry. This is useful when a tool must write to the file in place but devenv should remain the source of truth.

New in version 2.2

Creating Files in Subdirectories

Files can be created in nested directories by specifying the path:

devenv.nix

{
  files = {
    ".config/app/settings.json".json = {
      theme = "dark";
    };

    "scripts/build.sh" = {
      text = "#!/bin/bash\nnpm run build";
      executable = true;
    };
  };
}

The parent directories will be created automatically if they don't exist.