Typst generates a PDF, I want to display it.

[kierun]

This is the current workflow I have:

1. main.typ is compiled into a PDF ← this works fine.
2. Zathura is called to display the PDF ← this works.

What I would like to happen is this:

In the second stage, I want these two things:

1. zathura to be called if and only if it is not currently running. Note that I might have other zathura processes running, so it has to be this specific one.
2. I want the zathura process to detach from the shell I am running, or at least run in the background.

This is what I have so far:

tasks:
  pdf:
    desc: Create a pdf of the main.
    cmds:
      - mkdir -p pdf
      - typst compile main.typ pdf/atlas.pdf
      - task: zathura
    sources:
      - **/*.typ
      - Taskfile.yml
    interactive: true
    generates:
      - pdf/atlas.pdf
    status:
      - test -d pdf
    method: checksum
  zathura:
    desc: Opens the current PDF with Zathura.
    cmds:
      - zathura pdf/atlas.pdf  # ← I suspect this is going to get much more complex!
    sources:
      - pdf/atlas.pdf

[kierun]

Well, this works.

- if ! pgrep -f "zathura pdf/atlas.pdf"; then bash -c "zathura pdf/atlas.pdf & disown"; fi # yamllint disable-line

Is there something different I could have done?

[Yuno15-bb]

Your one-liner works, but three things can be simpler.

1. zathura can detach itself. zathura --fork FILE starts a copy of itself in a new session (setsid) and returns right away, so you don't need bash -c "… & disown". The copy runs as zathura FILE (without --fork), so a pgrep -f "zathura FILE" still finds it. man page, source

2. Put the "is it already running?" check in status:. That is what status is for: if the command succeeds, Task skips the task and prints Task "view" is up to date.

3. Make the viewer its own task that depends on the PDF. In your current layout, task: zathura is one of the pdf commands. When the PDF is up to date, Task skips the whole pdf task, so if you closed zathura and nothing changed, task pdf doesn't open it again.

version: '3'

tasks:
  pdf:
    desc: Create a pdf of the main.
    cmds:
      - mkdir -p pdf
      - typst compile main.typ pdf/atlas.pdf
    sources:
      - '**/*.typ'
      - Taskfile.yml
    generates:
      - pdf/atlas.pdf

  view:
    desc: Build the PDF, and open it unless it is already open.
    deps: [pdf]
    cmds:
      - zathura --fork pdf/atlas.pdf
    status:
      - pgrep -f "zathura pdf/atlas.pdf"

Also note that **/*.typ must be quoted: unquoted, YAML reads * as an alias and Task fails with did not find expected alphabetic or numeric character.

Why a plain zathura pdf/atlas.pdf & doesn't do it: Task runs commands with its built-in shell, which doesn't wait for background jobs. Task exits before the job has even started, so the viewer never opens. Anything that starts the process before returning works (zathura --fork, or sh -c 'zathura pdf/atlas.pdf >/dev/null 2>&1 &'); disown isn't what makes your version work.

How I checked, with Task 3.53.1 on macOS and a stand-in viewer (a script that sleeps, since I don't have zathura there):

• viewer & as a command: the viewer was never running afterwards, 5 runs out of 5. Adding sleep 0.2 after it was enough for it to start and stay up.
• sh -c 'viewer … &' and your bash -c "… & disown": still running after Task exited.
• The Taskfile above: first run builds and opens; second run prints both tasks as up to date and opens nothing; after editing main.typ it rebuilds without a second viewer; after closing the viewer it opens it again.
• Your layout: after closing the viewer with nothing changed, task pdf only printed Task "pdf" is up to date.

The --fork part comes from zathura's source, not from a run.

[kierun]

Thank you so much for this. It's awesome. 😀

[Yuno15-bb]

Always a pleasure to help French brother !

[kierun]

Always a pleasure to help French brother !

Merci! C'était très sympa!