Fix asdf $PATH loading in tmux on fish shell

Recently, I've been working on upgrading my React Native from 0.75.5 to the new architecture 0.81.1 and I had to upgrade my ruby version to 3. I've used nvm a lot before, thus I tried rvm, but for some reason the gpg keys installation step got stuck. So I decided to go with asdf instead, and it worked.

# Install asdf using brew
brew install asdf

# Install fish-asdf so that asdf works in fish shell
fisher install rstacruz/fish-asdf

# Add ruby plugin
asdf plugin add ruby

# Install latest ruby version
asdf install ruby latest

# Set global ruby version
asdf set --home ruby latest

# Set asdf shims path
asdf shims

# Check ruby location
which ruby # ~/.asdf/shims/ruby

# Check ruby version
ruby -v # ruby 3.4.6

My dev environment setup involves tmux heavily and I use fish shell. As soon as I opened a new session and started to work on my upgrade, it was weird.

# Launch a tmux session
tmux

# Check ruby version
ruby -v # 2.6.10

Wait a minute! Why is it showing ruby version 2.6.10, not the newly installed 3.4.6? And when I checked which ruby, as it turned out, it pointed to /usr/bin/ruby.

# Check ruby location
which ruby # /usr/bin/ruby

So I did some digging and found out that the 2.6.10 version came with macOS at /usr/bin/ruby. This issue only happened in tmux session because for some reason /usr/bin is loaded before ~/.asdf/shims in $PATH.

To fix this, I added the following snippet to my fish config ~/.config/fish/config.fish:

# Asdf
if test -z $ASDF_DATA_DIR
  set _asdf_shims "$HOME/.asdf/shims"
else
  set _asdf_shims "$ASDF_DATA_DIR/shims"
end

set -gx --prepend PATH $_asdf_shims
set --erase _asdf_shims

What this does is that ~/.asdf/shims is prepended to the $PATH which makes ruby load from ~/.asdf/shims instead of /usr/bin/ruby.

Now when I open a new tmux session and run ruby -v, it shows the 3.4.6 consistently.

# Check ruby version
ruby -v # ruby 3.4.6

So that's it, it works!