Standard Library Overview and Usage

# Standard Library (Preview) Nushell ships with a standard library of useful commands written in native Nu. By default, the standard library is loaded into memory (but not automatically imported) when Nushell starts. [[toc]] ## Overview The standard library currently includes: - Assertions - An alternative `help` system with support for completions. - Additional JSON variant formats - XML Access - Logging - And more To see a complete list of the commands available in the standard library, run the following: ```nu nu -c " use std scope commands | where name =~ '^std ' | select name description extra_description | wrap 'Standard Library Commands' | table -e " ``` ::: note The `use std` command above loads the entire standard library so that you can see all of the commands at once. This is typically not how it will be used (more info below). It is also run in a separate Nu subshell simply so that it is not loaded into scope in the shell you are using. ::: ## Importing the Standard Library The Standard Library modules and submodules are imported with the [`use`](/commands/docs/use.md) command, just as any other module. See [Using Modules](./modules/using_modules.md) for more information. While working at the commandline, it can be convenient to load the entire standard library using: ```nu use std * ``` However, this form should be avoided in custom commands and scripts since it has the longest load time. ::: important Optimal Startup when Using the Standard Library See the [notes below](#optimal-startup) on how to ensure that your configuration isn't loading the entire Standard Library. ::: ### Importing Submodules Each submodule of the standard library can be loaded separately. Again, _for best performance, load only the submodule(s) that you need in your code._ See [Importing Modules](./modules/using_modules.md#importing-modules) for general information on using modules. The recommended import for each of the Standard Library submodules is listed below: #### 1. Submodules with `<command> <subcommand>` form These submodules are normally imported with `use std/<submodule>` (without a glob/`*`): - `use std/assert`: `assert` and its subcommands - `use std/bench`: The benchmarking command `bench` - `use std/dirs`: The directory stack command `dirs` and its subcommands - `use std/input`: The `input display` command - `use std/help`: An alternative version of the `help` command and its subcommands which supports completion and other features - `use std/iters`: Additional `iters`-prefixed iteration commands. - `use std/log`: The `log <subcommands>` such as `log warning <msg>` - `use std/math`: Mathematical constants such as `$math.E`. These can also be imported as definitions as in Form #2 below. #### 2. Import the _definitions_ (contents) of the module directly Some submodules are easier to use when their definitions (commands, aliases, constants, etc.) are loaded into the current scope. For instance: ```nu use std/formats * ls | to jsonl ``` Submodules that are normally imported with `use std/<submodule> *` (**with** a glob/`*`): - `use std/dt *`: Additional commands for working with `date` values - `use std/formats *`: Additional `to` and `from` format conversions - `use std/math *`: The math constants without a prefix, such as `$E`. Note that the prefixed form #1 above is likely more understandable when reading and maintaining code. - `use std/xml *`: Additional commands for working with XML data #### 3. `use std <submodule>` It is _possible_ to import Standard Library submodules using a space-separated form: ```nu use std log use std formats * ```

Nushell includes a standard library of useful commands written in Nu. It covers assertions, an alternative help system, JSON variant formats, XML access, and logging. The library is loaded into memory upon Nushell's startup, and its submodules can be imported using the 'use' command. Submodules can be imported for the commands they add (like 'use std/assert'), or to import the definitions (commands, aliases, constants) directly into the current scope, with `use std/<submodule> *` (like `use std/formats *`).