Re-Inventing Task Runner That I Actually Used Daily

post, May 31, 2023 on Mitja Felicijan's blog

Couple of months ago I had this brilliant idea of re-inventing the wheel by making an alternative for make. And so I went. Boldly into the battle. And to my big surprise my attempt resulted in not a completely useless piece of software.

My initial requirements were quite simple but soon grow into something more ambitious. And looking back I should have stuck to the simple version. My laziness was on my side this time though. Because I haven’t implemented some of the features I now realise I really didn’t need them and they would bog the whole program and make it be something it was never meant to be.

My basic requirements were following:

  • Syntax should be a tiny bit inspired by Rake and Rakefiles.
  • Should borrow the overall feel of a unit test experience.
  • Using something like Python would be a bit of an overkill.
  • The program must be statically compiled, so it can run on same architecture without libc, musl dependencies or things like that.
  • Install ruby for rake is a bit overkill and can not be done with certain really lightweight distributions like Alpine Linux. This tool would be usable on such lightweight systems for remote debugging.
  • I want to use it for more than just compiling things. I want to use it as an entry-point into a project, and I want this to help me indirectly document the project as well.
  • It should be an abstraction over bash shell or the default system shell.
    • Each task essentially becomes its own shell instance.
  • Must work on Linux and macOS systems.
  • By default, running erd list all the available tasks (when I use make, I usually put a disclaimer that you should check Makefile to see all available target).
  • Should support passing arguments when you run it from a shell.
  • Normal variable as the same as environmental variables. There is no distinction. Every variable is also essentially an environment variable and can be used by other programs.
  • State between tasks is not shared, and this makes this “pure” shell instances.
  • Should be single-threaded for the start and later expanded with @spawn command.
  • Variables behave like macros and are preprocessed before evaluation.
  • Should support something like assure that would check if programs like C compiler or Python (whatever the project requires) are installed on a machine.

Quite a reasonable list of requirements. I do this things already in my Makefiles or/and Bash scripts. But I would like to avoid repeating myself every time I start working on something new.

So I started with the following syntax.

@env on

# Override the default shell.
@shell /bin/bash

# Assure that program is installed.
@assure docker-compose pip python3

# Load local dotenv files (these are then globally available).
@dotenv .env
@dotenv .env.sample
@dotenv some_other_file

# This are local variables but still accessible in tasks.
@var HI = "hey"
@var TOKEN = "sometoken"
@var EMAIL = ""
@var PASSWORD = "pass"
@var EDITOR = "vim"

@task dev "Test chars .:'}{]!//" does
  echo "..." $HI

@task clean "Cleans the obj files" does
  rm .obj

@task greet "Greets the user" does
  echo "Hi user $TOKEN or $WINDOWID $EMAIL"

@task stack "Starts Docker stack" does
  docker-compose -f stack.yml up

@task todo "Shows all todos in source files and count them" does
  grep -ir "TODO|FIXME" . | wc -l

@task test1 "For testing 1" does
  echo "test1"
  ls -lha

@task test2 "For testing 2" does
  echo "test1"
  ls -lha
  docker-compose -f samples/stack.yml up

One thing that I really like about Errand. Yes, this is what it is called. And it is available at Moving on. One thing that I really like is that a task is a persistent shell. By that I mean, that the whole task, even if it contains multiple command in one shell. In make each line in a target is that and you need to combine lines or add \ at the end of the line.

# How you do this things in make.
	source .venv/bin/activate \

This solves this problem. Consider each task and what is being executed in that task a shell that will only close when all the tasks are completed.

By self-documenting I mean that if you are in a directory with Errandfile in, if you only type erd and press enter it should by default display all the possible targets. In make i was doing this by having a first target be something like default that echos the message “Check Makefile for all available target.” Because all of the tasks in Errand require a message I use that to display let’s call it table of contents.

Because I don’t use any external dependencies this whole thing can be statically compiled. So that also checked one of the boxes.

It works on Linux and on a Mac so that’s also a bonus. I don’t believe this would work on Windows machines because of the way that I use shell instances. By you could use something like Windows Subsystem for Linux and run it in there. That is a valid option.

To finish this essay off, how was it to use it in “real life”. I have to be honest. Some of the missing features still bother me. @dotenv directive is still missing and I need to implement this ASAP.

Another thing that needs to happen is support for streaming output. Currently commands like docker-compose that runs in foreground mode is not compatible with Errand. So commands that stream output are an issue. I need to revisit how I initiate shell and how I read stdout and stderr. But that shouldn’t be a problem.

I have been very satisfied with this thing. I am pleasantly surprised by how useful it is. I really wanted to test this in the wild before I commit to it. I have more abandoned project than Google and it’s bringing a massive shame to my family at this point. So I wanted to be sure that this is even useful. And it actually is. Quite surprised at myself.

I really need to package this now and write proper docs. And maybe rewrite tokeniser. Its atrocious right now. Site to behold! But that is an issue for another time.