mirror of
https://github.com/nushell/nushell.git
synced 2024-12-23 15:39:06 +01:00
104 lines
5.1 KiB
Markdown
104 lines
5.1 KiB
Markdown
# Environment Variables (addition explaining the Values part)
|
|
|
|
(this is supposed to go to the Environment book chapter)
|
|
|
|
## Environment Variables Are Values
|
|
|
|
Since Nushell extends the idea of classic shells "Everything is a text" into "Everything is a structured data", it feels natural to apply this philosophy to environment variables as well.
|
|
In Nushell, environment variables can hold any value, not just a string.
|
|
|
|
Since the host environment (i.e., the OS Nushell is running in) treats environment variables as strings, we need a way to convert them between strings and arbitrary values seamlessly.
|
|
In general, there are two places when Nushell needs to interact with the host environment:
|
|
1. On startup, Nushell inherits the host environment variables.
|
|
2. When running an external program that is not part of Nushell's commands, the program expects environment variables to be strings.
|
|
3. When an environment variable is passed to an extenal library in the Nushell's codebase (this includes plugins as well). These variables are listed later in this section.
|
|
|
|
## Configuration
|
|
|
|
By default, if you do not configure anything, all environment variables are imported as strings on startup and then directly passed to any external program we might be spawning.
|
|
However, you can configure selected any environment variable to be converted to/from any value:
|
|
|
|
```
|
|
# config.nu
|
|
|
|
let config = {
|
|
... other config ...
|
|
env_conversions: {
|
|
FOO: {
|
|
from_string: {|s| $s | split row ':' }
|
|
to_string: {|v| $v | str collect ':' }
|
|
}
|
|
}
|
|
}
|
|
```
|
|
|
|
The above snippet will configure Nushell to run the `from_string` block with the `FOO` environment variable value as an argument on startup.
|
|
Whenever we run some external tool, the `to_string` block will be called with `FOO` as the argument and the result passed to the tool.
|
|
You can test the conversions by manually calling them:
|
|
|
|
```
|
|
> let-env FOO = "a:b:c"
|
|
|
|
> let list = (do $config.env_conversions.from_string $env.FOO)
|
|
|
|
> $list
|
|
╭───┬───╮
|
|
│ 0 │ a │
|
|
│ 1 │ b │
|
|
│ 2 │ c │
|
|
╰───┴───╯
|
|
|
|
> do $config.env_conversions.to_string $list
|
|
a:b:c
|
|
```
|
|
|
|
To verify the conversion works on startup, you can first set up `FOO`, then launch a new instance of Nushell (denoted as `>>`):
|
|
```
|
|
> let-env FOO = "a:b:c"
|
|
|
|
> nu
|
|
|
|
>> $env.FOO
|
|
╭───┬───╮
|
|
│ 0 │ a │
|
|
│ 1 │ b │
|
|
│ 2 │ c │
|
|
╰───┴───╯
|
|
```
|
|
|
|
To verify we're sending the correct value to an external tool, we would need to make a small program or script that prints its environment variables.
|
|
This is not hard, but we have a built-in command `env` to help.
|
|
Let's continue the previous session:
|
|
|
|
```
|
|
>> env
|
|
╭────┬───────────────────┬───────────────┬───────────────────┬───────────────────╮
|
|
│ # │ name │ type │ value │ raw │
|
|
├────┼───────────────────┼───────────────┼───────────────────┼───────────────────┤
|
|
│ 0 │ ... │ ... │ ... │ ... │
|
|
│ X │ FOO │ list<unknown> │ [list 3 items] │ a:b:c │
|
|
│ Y │ ... │ ... │ ... │ ... │
|
|
╰────┴───────────────────┴───────────────┴───────────────────┴───────────────────╯
|
|
```
|
|
|
|
The `env` command will print every environment variable, its value and a type and also the translated value as a string under the `raw` column.
|
|
The `raw` values is the values external tools will see when spawned from Nushell.
|
|
|
|
## Special Variables
|
|
|
|
Out of the box, Nushell ships with several environment variables serving a special purpose:
|
|
* `PROMPT_COMMAND` (block): To set the prompt. Every time Nushell REPL enters a new line, it will run the block stored as its value and set the result as the prompt.
|
|
* `PATH`/`Path`: Not yet used except passthrough to externals but is planned to support both its string and list forms.
|
|
* `LS_COLORS`: Sets up file coloring rules when running `ls` or `grid`. Supports `env_conversions` settings.
|
|
|
|
|
|
## Breaking Changes
|
|
|
|
* Setting environment variable to `$nothing` will no longer remove it -- it will be `$nothing`. Instead, you can use `hide $env.FOO`.
|
|
* `$env.PROMPT_COMMAND` is a block instead of a string containing the source of the command to run. You can put this into your `config.nu`, for example: `let-env PROMPT_COMMAND = { echo "foo" }`.
|
|
|
|
## Future Directions
|
|
|
|
* We might add default conversion of PATH/Path environment variables between a list and a string.
|
|
* We can make Nushell recognize both PATH and Path (and throw an error if they are both set and have different values?).
|