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| 1 | +# Special Variables |
| 2 | + |
| 3 | +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 |
| 4 | +should include _all_ variables for reference. |
| 5 | + |
| 6 | +[[toc]] |
| 7 | + |
| 8 | +## `$nu` |
| 9 | + |
| 10 | +The `$nu` constant is a record containing several useful values: |
| 11 | + |
| 12 | +- `default-config-dir`: The directory where the configuration files are stored and read. |
| 13 | +- `config-path`: The path of the main Nushell config file, normally `config.nu` in the config directory. |
| 14 | +- `env-path`: The optional environment config file, normally `env.nu` in the config directory. |
| 15 | +- `history-path`: The text or SQLite file storing the command history. |
| 16 | +- `loginshell-path`: The optional config file which runs for login shells, normally `login.nu` in the config directory. |
| 17 | +- `plugin-path`: The plugin registry file, normally `plugin.msgpackz` in the config directory. |
| 18 | +- `home-path`: The user's home directory which can be accessed using the shorthand `~`. |
| 19 | +- `data-dir`: The data directory for Nushell, which includes the `./vendor/autoload` directories loaded at startup and other user data. |
| 20 | +- `cache-dir`: A directory for non-essential (cached) data. |
| 21 | +- `vendor-autoload-dirs`: A list of directories where third-party applications should install configuration files that will be auto-loaded during startup. |
| 22 | +- `user-autoload-dirs`: A list of directories where the user may create additional configuration files which will be auto-loaded during startup. |
| 23 | +- `temp-path`: A path for temporary files that should be writeable by the user. |
| 24 | +- `pid`: The PID of the currently running Nushell process. |
| 25 | +- `os-info`: Information about the host operating system. |
| 26 | +- `startup-time`: The amount of time (in duration) that it took for Nushell to start and process all configuration files. |
| 27 | +- `is-interactive`: A boolean indicating whether Nushell was started as an interactive shell (`true`) or is running a script or command-string. For example: |
| 28 | + |
| 29 | + ```nu |
| 30 | + $nu.is-interactive |
| 31 | + # => true |
| 32 | + nu -c "$nu.is-interactive" |
| 33 | + # => false |
| 34 | +
|
| 35 | + # Force interactive with --interactive (-i) |
| 36 | + nu -i -c "$nu.is-interactive" |
| 37 | + # => true |
| 38 | + ``` |
| 39 | + |
| 40 | + Note: When started as an interactive shell, startup config files are processed. When started as a non-interactive shell, no config files are read unless explicitly called via flag. |
| 41 | + |
| 42 | +- `is-login`: Indicates whether or not Nushell was started as a login shell. |
| 43 | +- `history-enabled`: History may be disabled via `nu --no-history`, in which case this constant will be `false`. |
| 44 | +- `current-exe`: The full path to the currently-running `nu` binary. Can be combined with `path dirname` (which is constant) to determine the directory where the binary is located. |
| 45 | + |
| 46 | +## `$env` |
| 47 | + |
| 48 | +`$env` is a special mutable variable containing the current environment variables. As with any process, the initial environment is inherited from the parent process which started `nu`. |
| 49 | + |
| 50 | +There are also several environment variables that Nushell uses for specific purposes: |
| 51 | + |
| 52 | +### `$env.config` |
| 53 | + |
| 54 | +`$env.config` is the main configuration record used in Nushell. Settings are documented in `config nu --doc`. |
| 55 | + |
| 56 | +### `$env.PATH` |
| 57 | + |
| 58 | +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. |
| 59 | + |
| 60 | +It is converted back to a string before running a child-process. |
| 61 | + |
| 62 | +### `$env.ENV_CONVERSIONS` |
| 63 | + |
| 64 | +Allows users to specify how to convert certain environment variables to Nushell types. See [ENV_CONVERSIONS](./configuration.md#env_conversions). |
| 65 | + |
| 66 | +### `$env.LAST_EXIT_CODE` |
| 67 | + |
| 68 | +The exit code of the last command, usually used for external commands — Equivalent to `$?` from POSIX. Note that this information is also made available to the `catch` block in a `try` expression for external commands. For instance: |
| 69 | + |
| 70 | +```nu |
| 71 | +^ls file-that-does-not-exist e> /dev/null |
| 72 | +$env.LAST_EXIT_CODE |
| 73 | +# => 2 |
| 74 | +
|
| 75 | +# or |
| 76 | +try { |
| 77 | + ^ls file-that-does-not-exist e> /dev/null |
| 78 | +} catch {|e| |
| 79 | + print $e.exit_code |
| 80 | +} |
| 81 | +# => 2 |
| 82 | +``` |
| 83 | + |
| 84 | +### `env.CMD_DURATION_MS` |
| 85 | + |
| 86 | +The amount of time in milliseconds that the previous command took to run. |
| 87 | + |
| 88 | +### `$env.NU_VERSION` |
| 89 | + |
| 90 | +The current Nushell version. The same as `(version).version`, but, as an environment variable, it is exported to and can be read by child processes. |
| 91 | + |
| 92 | +### `$env.CURRENT_FILE` |
| 93 | + |
| 94 | +Inside a script, module, or sourced-file, this variable holds the fully-qualified filename. Note that this |
| 95 | +information is also available as a constant through the [`path self`](/commands/docs/path_self.md) command. |
| 96 | + |
| 97 | +### `$env.FILE_PWD` |
| 98 | + |
| 99 | +Inside a script, module, or sourced-file, this variable holds the fully qualified name of the directory in which |
| 100 | +the file resides. Note that this value is also available as a constant through: |
| 101 | + |
| 102 | +```nu |
| 103 | +path self | path dirname |
| 104 | +``` |
| 105 | + |
| 106 | +### `$env.PROCESS_PATH` |
| 107 | + |
| 108 | +When _executing a script_, this variable represents the name and relative path of the script. Unlike the two variables |
| 109 | +above, it is not present when sourcing a file or importing a module. |
| 110 | + |
| 111 | +Note: Also unlike the two variables above, the exact path (including symlinks) that was used to _invoke_ the file is returned. |
| 112 | + |
| 113 | +### `$env.NU_LIB_DIRS` |
| 114 | + |
| 115 | +A list of directories which will be searched when using the `source`, `use`, or `overlay use` commands. See also: |
| 116 | + |
| 117 | +- The `$NU_LIB_DIRS` constant below |
| 118 | +- [Module Path](./modules/using_modules.md#module-path) |
| 119 | +- [Configuration - `$NU_LIB_DIRS`](./configuration.md#nu_lib_dirs-constant) |
| 120 | + |
| 121 | +### `$env.NU_PLUGIN_DIRS` |
| 122 | + |
| 123 | +A list of directories which will be searched when registering plugins with `plugin add`. See also: |
| 124 | + |
| 125 | +- [Plugin Search Path](./plugins.md#plugin-search-path) |
| 126 | + |
| 127 | +### `$env.PROMPT_*` and `$env.TRANSIENT_PROMPT_*` |
| 128 | + |
| 129 | +A number of variables are available for configuring the Nushell prompt that appears on each commandline. See also: |
| 130 | + |
| 131 | +- [Configuration - Prompt Configuration](./configuration.md#prompt-configuration) |
| 132 | +- `config nu --doc` |
| 133 | + |
| 134 | +### `$env.SHLVL` |
| 135 | + |
| 136 | +`SHLVL` is incremented by most shells when entering a new subshell. It can be used to determine the number of nested shells. For instance, |
| 137 | +if `$env.SHLVL == 2` then typing `exit` should return you to a parent shell. |
| 138 | + |
| 139 | +### `$env.XDG_CONFIG_HOME` |
| 140 | + |
| 141 | +Can be used to optionally override the `$nu.default-config-dir` location. See [Configuration - Startup Variables](./configuration.md#startup-variables). |
| 142 | + |
| 143 | +### `$env.XDG_DATA_DIR` |
| 144 | + |
| 145 | +Can be used to optionally override the `$nu.data-dir` location. See [Configuration - Startup Variables](./configuration.md#startup-variables). |
| 146 | + |
| 147 | +## `$in` |
| 148 | + |
| 149 | +The `$in` variable represents the pipeline input into an expression. See [Pipelines - The Special `$in` Variable](./pipelines.md#pipeline-input-and-the-special-in-variable). |
| 150 | + |
| 151 | +## `$it` |
| 152 | + |
| 153 | +`$it` is a special variable that is _only_ available in a `where` "row condition" — a convenient shorthand which simplifies field access. See `help where` for more information. |
| 154 | + |
| 155 | +## `$NU_LIB_DIRS` |
| 156 | + |
| 157 | +A constant version of `$env.NU_LIB_DIRS` - a list of directories which will be searched when using the `source`, `use`, or `overlay use` commands. See also: |
| 158 | + |
| 159 | +- [Module Path](./modules/using_modules.md#module-path) |
| 160 | +- [Configuration - `$NU_LIB_DIRS`](./configuration.md#nu_lib_dirs-constant) |
| 161 | + |
| 162 | +## `$NU_PLUGIN_DIRS` |
| 163 | + |
| 164 | +A constant version of `$env.NU_PLUGIN_DIRS` - a list of directories which will be searched when registering plugins with `plugin add`. See also: |
| 165 | + |
| 166 | +- [Plugin Search Path](./plugins.md#plugin-search-path) |
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