# Special Variables

Nushell makes available and uses a number of special variables and constants. Many of these are mentioned or documented in other places in this Book, but this page
should include _all_ variables for reference.

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## `$nu`

The `$nu` constant is a record containing several useful values:

- `default-config-dir`: The directory where the configuration files are stored and read.
- `config-path`: The path of the main Nushell config file, normally `config.nu` in the config directory.
- `env-path`: The optional environment config file, normally `env.nu` in the config directory.
- `history-path`: The text or SQLite file storing the command history.
- `loginshell-path`: The optional config file which runs for login shells, normally `login.nu` in the config directory.
- `plugin-path`: The plugin registry file, normally `plugin.msgpackz` in the config directory.
- `home-path`: The user's home directory which can be accessed using the shorthand `~`.
- `data-dir`: The data directory for Nushell, which includes the `./vendor/autoload` directories loaded at startup and other user data.
- `cache-dir`: A directory for non-essential (cached) data.
- `vendor-autoload-dirs`: A list of directories where third-party applications should install configuration files that will be auto-loaded during startup.
- `user-autoload-dirs`: A list of directories where the user may create additional configuration files which will be auto-loaded during startup.
- `temp-path`: A path for temporary files that should be writeable by the user.
- `pid`: The PID of the currently running Nushell process.
- `os-info`: Information about the host operating system.
- `startup-time`: The amount of time (in duration) that it took for Nushell to start and process all configuration files.
- `is-interactive`: A boolean indicating whether Nushell was started as an interactive shell (`true`) or is running a script or command-string. For example:

  ```nu
  $nu.is-interactive
  # => true
  nu -c "$nu.is-interactive"
  # => false

  # Force interactive with --interactive (-i)
  nu -i -c "$nu.is-interactive"
  # => true
  ```

  Note: When started as an interactive shell, startup config files are processed. When started as a non-interactive shell, no config files are read unless explicitly called via flag.

- `is-login`: Indicates whether or not Nushell was started as a login shell.
- `history-enabled`: History may be disabled via `nu --no-history`, in which case this constant will be `false`.
- `current-exe`: The full path to the currently-running `nu` binary. Can be combined with `path dirname` (which is constant) to determine the directory where the binary is located.

## `$env`

`$env` is a special mutable variable containing the current environment variables. As with any process, the initial environment is inherited from the parent process which started `nu`.

There are also several environment variables that Nushell uses for specific purposes:

### `$env.config`

`$env.config` is the main configuration record used in Nushell. Settings are documented in `config nu --doc`.

### `$env.PATH`

The search path for executing other applications. It is initially inherited from the parent process as a string, but converted to a Nushell `list` at startup for easy access.

It is converted back to a string before running a child-process.

### `$env.ENV_CONVERSIONS`

Allows users to specify how to convert certain environment variables to Nushell types. See [ENV_CONVERSIONS](./configuration.md#env-conversions).

### `$env.LAST_EXIT_CODE`

The exit code of the last command, usually used for external commands — Equivalent to `$?` from POSIX. Note that this information is also made available to the `catch` block in a `try` expression for external commands. For instance: