Can I reference variables in exec backticks, or use no-cd somehow?

[patmaddox]

I want to set a variable like:

fossil-branch := `fossil branch current`

the rub is that I want it to run in invocation_directory() rather than the justfile directory.

I tried

# variable - shell syntax error
fossil-branch := `cd {{invocation_directory()}} && fossil branch current`

# [no-cd] - not a thing for variables
[no-cd]
fossil-branch := `fossil branch current`

I also tried [no-cd] on the command itself, thinking maybe it would apply that when evaluating the variable. It doesn't, and I can see how it may be ambiguous if you had dependencies where one command had [no-cd] and the other didn't.

Here are the commands I've written:

# export fossil wiki page for the current branch
[no-cd]
export-wiki:
  fossil wiki export branch/$(fossil branch current) wiki-branch-$(fossil branch current).md

# commit fossil wiki page for the current branch
[no-cd]
commit-wiki:
  fossil wiki commit -M markdown branch/$(fossil branch current) wiki-branch-$(fossil branch current).md || fossil wiki create -M markdown branch/$(fossil branch current) wiki-branch-$(fossil branch current).md

I'd like to consolidate it to something similar to:

# whatever is needed to get this in invocation_directory()
fossil-branch := `fossil branch current`
fossil-branch-wiki := 'wiki-branch-' + fossil-branch + '.md'

# commit fossil wiki page for the current branch
[no-cd]
export-wiki:
  fossil wiki export branch/{{fossil-branch}} {{fossil-branch-wiki}}

# export fossil wiki page for the current branch
[no-cd]
commit-wiki:
  fossil wiki commit -M markdown branch/{{fossil-branch}} {{fossil-branch-wiki}} || fossil wiki create -M markdown branch/{{fossil-branch}} {{fossil-branch-wiki}}

Is there a way to do that?

[runeimp]

First, where are the closing curly braces in

# variable - shell syntax error
fossil-branch := `cd {{invocation_directory() && fossil branch current`
...

I believe it should be

# variable - shell syntax error
fossil-branch := `cd {{invocation_directory()}} && fossil branch current`
...

Second, what shell are you using, CMD, sh, Bash, Elvish, Fish, Ion, Murex, Nu, PowerShell, Vsh, Zsh, etc. ?

[patmaddox]

First, where are the closing curly braces in

That was a transcription error as I wrote the post. Correcting curly braces makes no difference:

myvar := `cd {{invocation_directory()}} && pwd`

printdir:
  @echo {{myvar}}

produces:

$ just
sh: Syntax error: "(" unexpected
error: Backtick failed with exit code 2
  |
1 | myvar := `cd {{invocation_directory()}} && pwd`

It appears that just is executing the backticks as-is, without substituting the {{invocation_directory()}} first.

Second, what shell are you using, CMD, sh, Bash, Elvish, Fish, Ion, Murex, Nu, PowerShell, Vsh, Zsh, etc. ?

sh(1)

[runeimp]

Yeah, it can take a minute to get used to it all. Maybe this example will help. Try the following code:

invokdir := invocation_directory()

printdir:
	#!/bin/sh
	echo '     raw: {{invocation_directory()}} (just in sh)'
	invokdir='{{invocation_directory()}} (just to sh var)'
	myvar=`cd ${invokdir} && pwd`
	echo "invokdir: {{invokdir}} (just Justfile body)"
	echo "invokdir: ${invokdir}"
	echo "   myvar: ${myvar} (pure sh)"

In this context the cd ${invokdir} && pwd is likely redundant depending on what your trying to accomplish with it. But that sort of thing will get clearer once you've had a little more time with Just. 😃

[patmaddox]

cd {{invocation_directory()}} && pw was just an example of the simplest thing to demonstrate the behavior of variables in backticks.

My goal is to define a variable that executes a command in the invocation directory. Relevant part of full example from original post:

fossil-branch := `cd {{invocation_directory()}} && fossil branch current`
fossil-branch-wiki := 'wiki-branch-' + fossil-branch + '.md'

so that I can use fossil-branch and fossil-branch-wiki in multiple commands.

I take it that just currently does not have a mechanism to accomplish that?

[runeimp]

No, not like you want currently. There are a few issues.

1. Variable names need to be camel case or snake case if you export them to shell. Otherwise the hyphenated names are fine.
2. Most of the code must reside in a recipe. It doesn't seem you can do && type logic in backticks, only piping in the Justfile body.

I looked into it more and I think this covers it best

fossil-path := invocation_directory()

# This recipe initializes and demonstrates the use of the fossil.vars file
_default: _term-wipe
	#!/bin/sh
	just _set_fossil_vars
	source '{{justfile_directory()}}/fossil.vars' # Source the vars into the scope of this recipe
	# Of course "." is more portable to "source files" but less readable

	echo 'fossil-path: "{{fossil-path}}"'
	echo "fossil_branch: ${fossil_branch}"
	echo "fossil_wiki: ${fossil_wiki}"

# Call this to initialize or update the fossil.vars file
_set_fossil_vars:
	#!/bin/sh
	cd '{{fossil-path}}'
	fossil_branch="$(fossil branch current)" # You can use backticks if you prefer here

	cd '{{justfile_directory()}}'
	echo "fossil_branch=${fossil_branch}" > fossil.vars # Initial file creation and creation of the first variable
	echo "fossil_wiki=wiki-branch-${fossil_branch}.md" >> fossil.vars # Adding another variable

Then you can source '{{justfile_directory()}}/fossil.vars' in any recipe you need those values in. For an alternative using Python see Sharing Environment Variables Between Recipes - Just Programmer's Manual.