Every so often I install a program via gem, npm or some other language
specific package manager and want it to be available globally on my system. Npm
has the -g flag but this doesn’t help when I change Node versions. The same
goes for Ruby. If I switch to a different version of Ruby I can’t use the
command I installed in the earlier version.
A concrete example of this is the excellent
Tmuxinator gem. The gem allows tmux
sessions to be defined in yaml files. When a project is opened with the
tmuxinator command it creates the session defined in the yaml file for the
project automatically. Since Tmuxinator is a gem it’s only available under the
version of Ruby it was installed in. If I change to a directory that’s set to
use a different version of Ruby my tmuxinator command won’t be available.
I really don’t want to have to install the same gem in every version of Ruby
I use. It would be wasteful to have multiple installations of the same gem and
upgrading all those installations would be a hassle.
Thankfully there is an easy way to handle this if you are using
asdf. asdf reads environment variables that
are in the format ASDF_<LANGUAGE>_VERSION. In our case this is a Ruby gem, so
we need to set ASDF_RUBY_VERSION to the right version of Ruby before
executing tmuxinator. To do this you can create a simple alias or shell
script. Either will work and both have their advantages. Aliases are shorter
and easier to create. Assuming you’ve installed Tmuxinator under Ruby 2.3.0 the
alias should look like this:
alias tmuxinator="ASDF_RUBY_VERSION=2.3.0 tmuxinator"
Just add that line to your .bashrc or .zshrc and you should have have
a tmuxinator alias that works in any directory, even directories that are set
to use different versions of Ruby. You can name the alias anything you want.
A different name may be useful if you want to differentiate this global
tmuxinator alias from another instance of tmuxinator installed on your system.
A slightly more involved solution is to use a shell script. Even this isn’t
that hard to do. All you need to do is create a file with the name you want the
command to have (just like the name of the alias above). The file should be
placed in a directory on you $PATH (I have $HOME/bin/ for scripts like
this). Then run chmod +x <filename> to set the execution permission for the
file. Finally open it up in your editor and enter in the following:
#!/usr/bin/env bash
export ASDF_RUBY_VERSION=2.3.0
exec tmuxinator
That’s it! This will work just like the alias, and if it’s on your $PATH it
will be available from every directory. The exec line tells Bash to execute
the actual tmuxinator program in the same process as the script, rather than
spawning another process as it normally would. This makes it slightly more
efficient than just calling tmuxinator directly.
References
- Tmuxinator: https://github.com/tmuxinator/tmuxinator
- asdf: https://github.com/asdf-vm/asdf
- Issue discussed on the rbenv issue tracker: https://github.com/rbenv/rbenv/issues/276