nur - a taskrunner based on nu shell

nur is a simple, yet very powerful task runner. It borrows ideas from b5 and just, but uses nu shell scripting to define the tasks. This allows for well-structured tasks.

Quick overview and example

nur allows you to execute tasks defined in a file called nurfile. It will look through your current working directory and all its parents to look for this file. When it has found the nurfile it will change to the directory the file was found in and then source the file into nu script. You can define tasks like this:

# Just tell anybody or the "world" hello
def "nur hello" [
    name: string = "world"  # The name to say hello to
] {
    print $"hello ($name)"
}

The important bit is that you define your tasks as subcommands for "nur". If you then execute nur hello it will print "hello world", meaning it did execute the task hello in your nurfile. You can also use nur --help to get some details on how to use nur and nur --help hello to see what this hello task accepts as parameters.

You may also pass arguments to your nur tasks, like using nur hello bob to pass "bob" as the name to the "hello" task. This supports all parameter variants normal nu scripts could also handle. You may use nur --help <task-name> to see the help for an available command.

Your tasks then can do whatever you want them to do in nu script. This allows for very structured usage of for example docker to run/manage your project needs. But it can also execute simple commands like you would normally do in your shell (like npm ci or something). nur is not tied to any programming language, packaging system or anything. As in the end the nurfile is basically a normal nu script you can put into this whatever you like.

I recommend reading "Working with nur" below to get an overview how to use nur. Also I recommend reading the nu documentation about custom commands for details on how to define nu commands (and nur tasks) and at least read through the nu quick tour to understand some basics and benefits about nu scripting.

Installing nur

As of now nur is not available using common package managers. This is however no issue as cargo allows you to install packages into your own user directory.

Note: You need to have cargo installed for this to work. See cargo install docs for details on getting cargo running.

Just run cargo install nur to install nur for your current user. The nur binary will be added in $HOME/.cargo/bin (or $"($env.HOME)/.cargo/bin" in nu shell). Make sure to add this to $PATH (or $env.PATH in nu shell).

Shell example (like Bash, zsh, ...):

> cargo install nur
> export PATH="$HOME/.cargo/bin:$PATH"  # put this into your .bashrc, .zshrc or similar
> nur --version

nu shell example:

> cargo install nur
> $env.PATH = ($env.PATH | split row (char esep) | prepend [$'($nu.home-path)/bin'])  # put this into $nu.env-path
> nur --version

Important: You do not need to have nu shell installed for nur to work. nur does include the whole nu runtime engine and will run as a standalone command.

Alternative installation methods

• For MacOS you can use my unofficial Homebrew tap to install nur. All necessary steps are documented in the repository: https://github.com/ddanier/nur-homebrew
  (This will allow you to just use brew install nur)
• For Windows you can just use the provided binaries available in each release version. Note the .msi package might be the easiest to use: https://github.com/ddanier/nur/releases

Working with nur

As shown above you can use subcommands to "nur" to add your tasks. This section will give you some more details and some hints how to do this in the best way possible.

About the nurfile

Your tasks are defined in a file called nurfile. This file is a normal nu script and may use nu commands to define nur tasks. All tasks must be defined as subcommands to "nur", you still will be able to define any other commands and use those as helpers in your tasks. Only subcommands to "nur" will be exposed by running nur.

In addition you may add a file called nurfile.local to define personal, additional tasks. I recommend adding the nurfile to git, while nurfile.local should be ignored. This allows each developer to have their own additional set of tasks.

Some basics about nur

nur tasks will always be run inside the directory the file nurfile was found in. If you place a nurfile in your project root (git root) you will be able to call tasks from anywhere inside the project. This is useful to always have a reproducible base setup for all your tasks.

nur will provide the internal state and config in the variable $nur, containing:

• $nur.run-path: The path nur was executed in
• $nur.project-path: The path nur executes the tasks in, this means the path the nurfile was found
• $nur.task-name: The main name of the task being executed, if any (Note: If you are running sub task this will not include the sub tasks names, use $env.NUR_TASK_NAME instead)

nur will also set the following ENV variables:

• NUR_VERSION: The version of nur being executed (similar to NU_VERSION)
• NUR_TASK_NAME: The full name of the task being executed, including sub tasks
• NUR_TASK_CALL: The full call to the task, including "nur" prefix and all arguments

Defining nur tasks

I highly recommend reading nu custom commands for more details, but I will try to show you the most important bits right here. I will use the term "nur task" to talk about subcommands to nur in the following section. If you know about nu, just know that the tasks are actually really only normal subcommands.

This means you define nur tasks like def "nur something" - which you can then call by using nur something. nur tasks can call any other nu commands or system command.

The most basic nur task could look like this:

def "nur hello-world" [] {
    print "Hello world"
}

nu commands are defined using the def keyword. The command name ("nur hello-world" in this case) is followed by the arguments. Those are written in square brackets ([ and ]), see next chapter for some details on arguments. The command body is then put into curly brackets and can contain any nu script code.

For the most tasks this means your nur task will just execute some system commands like poetry install or npm ci or cargo publish or something similar - but you can also create more complex tasks, however you like. You may look into the nurfile of nur itself for some examples.

nu commands will use the result of the last line in the command body as the command return value. nur will then automatically print the return values of the task. The importand thing to understand is that nu will see the output of a command as its return value. So this is also true for any command output written to stdout, the output of the last line in your command will be used as the command result/output and thus printed by nur. Any other commands that have been run in your command function will be eaten by nu, unless you actively use print (command | print or print (command)).

This behaviour of nu commands may be strange at first glance, but makes a lot of sense when working with pipelines the way nu does. Having any output produced by each line in a command definition be redirected mixed output and result in errors handling the results. When using nu scripts for nur tasks you need to know about this behaviour and handle any additional output you want to produce accordingly.

An example using print:

def "nur do-something-useful" [] {
    print "We will do something useful now:"
    run-command-1 | print
    print "Now more useful stuff:"    
    run-command-2 | print  # you can also skip the `print` here, as it is the last line
}

If your command should not produce any output you can return null.

Adding some arguments to your tasks

nur tasks can receive three different kinds of arguments:

• Named, positional arguments: def "nur taskname" [argument1, argument2] { ... }
  • Adding a ? after the parameter name makes it optional
  • Above example provides the variables $argument1 and $argument2 in the task
• Flags as parameters: def "nur taskname" [--argument1: string, --argument-number2: int] { ... }
  • If you want to have named flags that can actually receive any values, you need to add a type (see below for typing)
  • Flags are always optional, default value will be null unless defined otherwise (see below for default values)
  • Flags will provide variables names without the leading --
  • Flags will be available in your task code as variables with all - replaced by _
  • Above example provides the variables $argument1 and $argument_number2 in the task
  • You may provide short version of flags by using --flag (-f)
• Boolean/switch flags: def "nur taskname" [--switch] { ... }
  • Boolean/switch flags must NOT be typed
  • Those can only receive the values true/false, with false being the default
  • Above example provides the variable $switch in the task
• Rest parameters might consume the rest of the arguments: def "nur taskname" [...rest] { ... }
  • Above example provides the variable $rest in the task

Arguments can (and should) be typed, you can use argument_name: type for doing so. A typed argument could look like this:
def "nur taskname" [argument1: string, argument2: int] { ... }
(see parameter types for a full list of available types)

Also arguments can have a default value, you can use argument_name = "value" to set the default value. An example using a default value could look like this:
def "nur taskname" [argument1 = "value", argument2 = 10] { ... }

Example with different kinds of arguments:

def "nur something" [
    name: string
    optional?: string
    --age (-a): int = 23
    --switch (-s)
] {
    null  # nothing here
}

Adding documentation to your command

You may add documentation by adding commands to your nur tasks. See the usage example above and the nu command documentation section.

Basic rule is that the commend right above your task will be used as a description for that task. Comments next to any argument will be used to document that argument.

Example task documentation:

# This is the documentation used for your task
# you may use multiple lines
#
# and use empty lines to structure the documentation (as long as it is one comment block)
def "nur something" [
    name: string  # This is used to document the argument "name" 
    --age: int  # This is used to document the argument "age" 
] {
    null  # nothing here
}

The above example will generate the following documentation when running nur --help something or nur something --help:

❯ nur --help something
This is the documentation used for your task
you may use multiple lines

and use empty lines to structure the documentation (as long as it is one comment block)

Usage:
  > nur something {flags} <name>

Flags:
  --age <Int> - This is used to document the argument "age"
  -h, --help - Display the help message for this command

Parameters:
  name <string>: This is used to document the argument "name"

Calling system commands from nur

If you want to run external commands you might run into the issue that nu itself provides some builtin commands that might match the name of the command you want to run. This for example is the case for sort, where nu has it's own version (see sort command). Most of the time it makes sense to use the versions nu provides as those implement all the pipeline improvements of nu. If you want to call the external command and not the builton function by nu use ^sort instead of sort in your nur tasks.

The same rule applies to your user defined functions, you would for example provide a function named grep (def grep [] { ... }) which could call the grep command using ^grep.

Example calling ls and sort system commands:

def "nur call-sort" [] {
    ^ls | ^sort
}

My recommendation would be to embrace the nu builtin commands and use the structured data those provide and consume as much as possible. See "Some notes about pipelines and how nu handles those" below for some more details on this.

Provide nur tasks for wrapping shell commands

If you want to use a nur to run and wrap any normal command - for example to ensure you can run this in any subdirectory of your project - I recommend using the following schema (using the poetry package manager as an example):

def --wrapped "nur poetry" [...args] {
    poetry ...$args
}

The important bit is using --wrapped, so the nu parser will not try to match flags starting with - into your nur task.

See the docs for def for some more details.

Some notes about pipelines and how nu handles those

Normal UNIX shells always use text to pass data from stdout (or stderr) to the next command via stdin. This is pretty easy to implement and a very slim contract to follow. nu however works quite different from this. Instead of passing test when using pipelines it tried to use structured data - think of this like passing JSON between the different command. This increases the flexibility and structured way to work with the data in a great way.

For example getting the ID of a running container in docker would look somewhat like this in a normal UNIX shell:

docker ps | grep some-name | head -n 1 | awk '{print $1}'

This works for most of the cases, but might produce errors for example of a container named this-also-contains-some-name-in-its-name exists. This issue exists as we are parsing text data, not some actual structured data. So having the name anywhere in a line will result in that line being used. (Note: I know about docker ps --filter ..., this is just to explain the overall issue of parsing text data)

nu works on structured data and provides commands to filter, sort or restructure that data in any way you like. Also nu provides mechanics to import text data into this structured format. Getting the docker ps text data input nu can for example be done using docker ps | from ssv ("ssv" stands for "space-separated values"), see the command from for more possible input formats.

To get the first container matching using the image some-name you could use this command:

docker ps | from ssv | where IMAGE == "some-name" | get "CONTAINER ID" | first

This is using the where command to match only a single row and then the get command to reduce the row to just one column. There are also many more commands to work with structured data.

This way of working with command data in a very structured form is very much superior to how normal shells used to work. This is especially good when you are creating more complex scripts and thus also true for the tasks you will write in your task runner. This is why I did choose nu for creating nur.

I recommend reading thinking in nu to get a grasp about this concept and start using nu script in nur in a very structured way. Also you may want to read the nu documentation on pipelines.

Using other custom commands in your nurfile

You can define any command you like and need to use. Just know that subcommands to "nur" will be available as tasks. All other commands will not be available.

def some-helper [] {
    do-something-useful
}

def "nur something" [] {
    print "Calling some-helper"
    some-helper
}

Using sub tasks for better structure

Like with normal nu shell commands nur can also handle sub commands and thus sub tasks.

def "nur something sub" [] {
    print "The sub task to something"
}

You could then just call nur something sub to run the sub task. This is a great way to organise your nurfile into different logical parts, for example when using a monorepo.

Organising your nur helpers into modules

If your helper commands get more sophisticated you may want to use a nu module instead of putting all of your code into one big nurfile. nur will automatically add the directory called .nur/scripts/ into $env.NU_LIB_DIRS. This allows you to define nu modules there and then use those in your nurfile.

Basic hello world example:

# .nur/scripts/hello-world.nu

export def main [] {
    print "Hello world"
}

# nurfile
use hello-world.nu

def "nur hello" [] {
    hello-world
}

I recommend reading about nu modules in the official nu documentation.

Provide env.nu and config.nu for project specific setup

Like with nu you can have your own environment and configuration files in nur. Unline nuthose don't live in your$HOME` folder but can be put into the project and as of this into version control. This also means you can have different configurations for different projects.

nur will load those files if they exist:

• .nur/env.nu for the environment
• .nur/config.nu for the configuration

The recommended usage is to put environment changes like changes to $env.NU_LIB_DIRS into env.nur. After this file was loaded those changes will already be active, allowing you to for example source or use modules from additional paths. Then you may use the config.nu to add project specific, but global, configuration.

See the nu documentation on env.nu and config.nu files for some more insights. You may use the default variants of both files as the base to do any modifications.

Advanced topics and further reading

You may also look into those nu topics:

• Commands
• Variables (also covers immutable/mutable variables)
• Operators
• Control flow
• Builtin commands
• Modules

Why I built nur + some history

For me nur is the next logical step after I created b5. b5 is based on running bash code and allowing users to do this in a somewhat ordered matter. Initially b5 even was just some bash script, but then eventually I figured bash is just not enough to handle my requirements. So I switched to using Python, but b5 was still based on bash, as it would generate bash code and then just execute the code. One issue I always had with this approach was that again bash isn't that nice to write complex things without introducing issues everywhere. Look for example at parameter handling.

Then along came just, which did implement its own language you could use to write your justfile. This language was inspired by what a Makefile would look like, still without the issues Makefile's impose when using those as your task runner. Also, it did include a very nice way to define task arguments, parse those, care about validation etc. Still the way just works is either to execute the task line by line (and not having any context between those commands) or define some script language to execute the full command (meaning using something like bash again). So just - at least for me - is a great step forward, but still not what I had in mind when creating b5 and what I would like to do with a task runner.

Then I came across nu, especially the nu shell. This did become my default shell after a while, and I am using it as of now. nu feels nicely designed, has a very structured way to execute commands and also handle their "response" data (stdout/err) - as everything is structured data there. This is way better than the original UNIX approach of always passing text data. Also nu allows you to have simple functions, that - as with just - handle argument parsing for you. So this did look like the perfect combination for something like a task runner.

Of course, you could just define some nu functions to completely create a task runner and that would already be better than b5 or just. But this would also mean that every dev using this task runner would need to switch to nu first. So I decided to try the hard route and create my own rust based cli tool that would parse a nu script and then execute tasks defined in this script.

This is what you are seeing here. nur will load the nurfile defined in your project directory and then allows you to execute tasks from this file. As it is its own binary you can easily use nur from bash, zsh and possibly even PowerShell - whatever you prefer. Still you will be able to have the nu superpowers inside your defined tasks.

About the name

nur stands for "nu run". Basically it should be "nu run task", which would lead to "nurt" - but then I decided for just "nur" as:

• nur is very fast to type (one less character 💪)
• nur is the reverse of run, which I like as a side effect 🥳
• and then as a nice and also weird side effect: You could translate "just" to "nur" in german 😂