nushell/crates/nu-utils/standard_library/README.md

<h1 align="center">
  Welcome to the standard library of `nushell`!
  <img src="https://media.giphy.com/media/hvRJCLFzcasrR4ia7z/giphy.gif" width="28"></img>
</h1>

The standard library is a pure-`nushell` collection of commands to allow anyone to build
complex applications using standardized tools gathered incrementally.

In this library, you might find `rust`-like `assert` commands to write tests, tools to
manipulate paths and strings, etc, etc, ...

## :toolbox: use the standard library in the REPL or in scripts
in order to "import" the standard library to either the interactive [*REPL*][REPL] of
`nushell` or inside some `.nu` script, you might want to use the
[`use`](https://nushell.sh/commands/docs/use.html) command!
```bash
use /path/to/standard_library/std.nu
```

> ### :mag: a concrete example
> - my name is @amtoine and i use the `ghq` tool to manage `git` projects
> > **Note**  
> > `ghq` stores any repository inside `$env.GHQ_ROOT` under `<host>/<owner>/<repo>/`
> - the path to my local fork of `nushell` is then defined as
> ```bash
> let-env NUSHELL_REPO = ($env.GHQ_ROOT | path join "github.com" "amtoine" "nushell")
> ```
> - and the full path to the standard library is defined as
> ```bash
> let-env STD_LIB = ($env.NUSHELL_REPO | path join "crates" "nu-utils" "standard_library")
> ```
> > see the content of `$env.STD_LIB` :yum:
> > ```bash
> > >_ ls $env.STD_LIB | get name | str replace $env.STD_LIB "" | str trim -l -c "/"
> > ╭───┬───────────╮
> > │ 0 │ README.md │
> > │ 1 │ std.nu    │
> > │ 2 │ tests.nu  │
> > ╰───┴───────────╯
> > ```
> - finally we can `use` the standard library and have access to the commands it exposes :thumbsup:
> ```bash
> >_ use std.nu
> >_ help std
> Module: std
>
> Exported commands:
>   assert (std assert), assert eq (std assert eq), assert ne (std assert ne), match (std match)
>
> This module does not export environment.
> ```

## :pencil2: contribute to the standard library
- all the commands of the standard_library are located in [`std.nu`](std.nu)
- the tests are located in files that have a name starting with "test_", e.g. [`test_std.nu`](test_std.nu)
- a test runner, at [`tests.nu`](tests.nu), allows to run all the tests automatically

### :wrench: add new commands
- add new standard commands by appending to [`std.nu`](std.nu)
- add associated tests to [`test_std.nu`](tests_std.nu) or preferably to `test_<submodule>.nu`.
    - define a new exported (!) `test_<feature>` command
    - import the `assert` functions you need at the top of the functions, e.g. `use std.nu "assert eq"`

### :test_tube: run the tests
the following call should return no errors
```bash
NU_LOG_LEVEL=DEBUG nu /path/to/standard_library/tests.nu
```

> #### :mag: a concrete example
> with `STD_LIB` defined as in the example above
> ```bash
> NU_LOG_LEVEL=DEBUG nu ($env.STD_LIB | path join "tests.nu")
> ```

[REPL]: https://en.wikipedia.org/wiki/Read%E2%80%93eval%E2%80%93print_loop