feat: add ujust, refactor shell change tasks

This adds a little shim, `/usr/bin/ujust`, to run,
`just --unstable --justfile /usr/share/ublue-os/justfile`.

I think this is a much cleaner way to run our `just` tasks than putting
a `~/.justfile` in the home directory, for a number of reasons. One of
them is that this does not require aliasing `just=just --unstable`, and
another is that a user can actually have their own `~/.justfile` with no
regard for including our global one.

I didn't remove the `just` aliases from the shell dotfiles, because I'm
not sure what breaking changes that might cause -- documentation, for sure,
but also does yafti or anything else depend on that?

Also to be honest I'm not sure where the default just alias comes from.
I didn't actually look yet :P

I did this because I realized how much duplicate code and room for errors
I had in the shell change tasks I rewrote -- I think it's much better to
write a task with an argument, `just chsh /usr/bin/newshell`, and then
call that from other tasks that need to change the shell. However, I saw
the limitations of using shell aliases to add the `--unstable` flag quite
quickly -- my sub-just-invocations became longer than I'd like them to be.
See https://just.systems/man/en/chapter_40.html and note how much nicer
that is than `just --unstable --file /usr/share/ublue-os/justfile`...

I'd definitely like to see others' thoughts on this! Feel free to ping me
on Discord @bri9.

--bri

just/custom.just

@@ -1,5 +1,7 @@
 # vim: set ft=make :
 
+uid := `id -u`
+
 # Run a one minute system benchmark
 benchmark:
   echo 'Running a 1 minute benchmark ...'
@@ -23,6 +25,10 @@ aqua:
   printf '\n    export PATH="${AQUA_ROOT_DIR:-${XDG_DATA_HOME:-$HOME/.local/share}/aquaproj-aqua}/bin:$PATH"\n'
   printf '\n=> see https://aquaproj.github.io/docs/tutorial for more info\n'
 
+# Set shell (back) to bash
+bash:
+  ujust chsh /bin/bash
+
 # Install Homebrew for Linux
 brew:
   echo "Installing homebrew ..."
@@ -38,18 +44,31 @@ brew-shell:
   if grep -q "linuxbrew" $HOME/.zprofile
   then
     echo "Brew configuration already present in .zprofile"
-  else 
+  else
     echo "Adding Brew configuration to .zprofile"
     echo 'eval "$(/var/home/linuxbrew/.linuxbrew/bin/brew shellenv)"' >> $HOME/.zprofile
   fi
   if grep -q "linuxbrew" $HOME/.bash_profile
   then
     echo "Brew configuration already present in .bash_profile"
-  else 
+  else
     echo "Adding Brew configuration to .bash_profile"
     echo 'eval "$(/var/home/linuxbrew/.linuxbrew/bin/brew shellenv)"' >> $HOME/.bash_profile
   fi
 
+# Change the user's shell
+chsh shell:
+  #!/usr/bin/env bash
+  set -euo pipefail
+  CURRENT_SHELL="$(cat /etc/passwd | grep ":{{uid}}:" | cut '-d:' '-f7')"
+  if [ "{{shell}}" = "${CURRENT_SHELL}" ] ; then
+    printf "Your shell is already set to %s.\n" "${CURRENT_SHELL}"
+  else
+    sudo usermod $USER --shell "{{shell}}"
+    CURRENT_SHELL="$(cat /etc/passwd | grep ":{{uid}}:" | cut '-d:' '-f7')"
+    printf "%s's shell is now %s.\n" "$USER" "${CURRENT_SHELL}"
+  fi
+
 # Enable Cockpit for web-based system management | https://cockpit-project.org/
 cockpit:
   echo 'Enabling Cockpit'
@@ -107,8 +126,7 @@ distrobox-universal:
 
 # Switch to the fish shell
 fish:
-  sudo usermod $USER --shell /usr/bin/fish 
-  printf "${USER}'s shell is now %s." "$(cat /etc/passwd | grep ":$UID:" | cut '-d:' '-f7')"
+  just --unstable --justfile {{justfile()}} chsh /usr/bin/fish
 
 # Install recommended GNOME extensions
 gnome-extensions:
@@ -154,12 +172,12 @@ nix-devbox-global:
 
 # Enable podmansh as user shell (EXPERIMENTAL)
 podmansh:
+  #!/usr/bin/env bash
   sudo mkdir -p /etc/containers/systemd/users/${UID}
   sudo cp /usr/share/ublue-os/quadlets/podmansh.container /etc/containers/systemd/users/${UID}/podmansh.container
-  sudo usermod $USER --shell /usr/bin/podmansh
-  printf "${USER}'s shell is now %s." "$(cat /etc/passwd | grep ":$UID:" | cut '-d:' '-f7')"
+  just --unstable --justfile {{justfile()}} chsh /usr/bin/podmansh
   podman pull ghcr.io/ublue-os/ubuntu-toolbox:latest
-  
+
   systemctl --user daemon-reload
   systemctl --user stop podmansh.service
   systemctl --user start podmansh.service
@@ -186,7 +204,7 @@ pytorch:
   --no-browser --allow-root"
 
 # Run Tensorflow
-tensorflow: 
+tensorflow:
   echo 'Follow the prompts and check the tutorial: https://www.tensorflow.org/tutorials/quickstart/beginner'
   podman pull docker.io/tensorflow/tensorflow:latest
   podman run -it -p 8888:8888 docker.io/tensorflow/tensorflow:latest-jupyter  # Start Jupyter server
@@ -217,8 +235,7 @@ yafti:
 
 # Switch to the zsh shell
 zsh:
-  sudo usermod $USER --shell /usr/bin/zsh 
-  printf "${USER}'s shell is now %s." "$(cat /etc/passwd | grep ":$UID:" | cut '-d:' '-f7')"
+  just /usr/bin/zsh
 
 docker:
   sudo systemctl enable --now docker

usr/bin/ujust

@@ -0,0 +1,2 @@
+#!/bin/sh
+/usr/bin/just --unstable --justfile /usr/share/ublue-os/justfile