Why I really like fish abbreviations

I'm filing this as a TIL because, while it wasn't T, I did L it very recently and it was a new trick that impacted on around 25 years if prior working practice.

I think it must have been around 1991 when I first encountered 4DOS. While I'd used the odd Unix shell here and there previously, it'd only been in passing. It was 4DOS that first introduced me to the power of aliases on the command line. Many of the aliases I set up and used in 4DOS still remain with me to this day, on GNU/Linux and macOS, in some form or another.

I'm sure I don't need to tell anyone reading this why aliases and cool and handy and pretty much vital if you do lots of work on the command line.

And then, a couple or so weeks ago, as a very recent convert to fish, I discovered the abbr command. At first glance it didn't seem to make much sense. It was like alias, only it expanded what you typed rather than acted as a command in its own right.

I did a bit of digging and some of it started to make sense. One thing that really won me over -- and while it's something that doesn't directly impact on me -- was the argument that it allows for a far more transparent command history; especially if you're likely to use a transcript of a shell session in a place where people might not know or have access to your aliases.

Imagine being in a position where you have loads of handy and cool aliases, but you also need to record what you've done so other people can follow your work (does it show that I sit amongst people who maintain lab notebooks?); it seems like it would be a bit of a bother needing to record all of the aliases in your own work environment up front. Without that information few people will be able to make sense of the recorded commands, with that information they'd still need to double-check what each command does.

So imagine an alias that, when used, expands in place. Then you'd get all of the benefit of aliases while also having a full and readable record of what you actually did.

Seems neat!

Here's a silly example. For a long time I've carried around an alias called greedy that runs something like this:

du -hs * | sort -rh

It's pretty straightforward: I'm using du to get a sense of which directories are using what space, and then using sort to make a worst-to-best-offender list out of it. So I could use an alias:

alias greedy="du -hs * | sort -rh"

The only downside to this is that, any time I run it, if I were to record the shell session and make it available for someone else to read, they'd just see:

~/develop$ greedy
1.1G    JavaScript
824M    C
699M    rust
 93M    python
 33M    fonts
 33M    elisp
3.4M    zsh
3.0M    misc
1.1M    bash
840K    ocaml
428K    C++
316K    lisp
172K    Swift
152K    git
132K    ruby
 28K    ObjC

Now, with an abbreviation rather than an alias, I'd type greedy but as soon as I hit Enter it'd get expanded to something anyone could read and follow:

~/develop$ du -hs * | sort -rh
1.1G    JavaScript
824M    C
699M    rust
 93M    python
 33M    fonts
 33M    elisp
3.4M    zsh
3.0M    misc
1.1M    bash
840K    ocaml
428K    C++
316K    lisp
172K    Swift
152K    git
132K    ruby
 28K    ObjC

This is far from the only benefit of abbreviations; for most people it probably isn't one of the most important ones, but I find it neat and compelling and this alone drove me to rework almost all of my aliases as abbreviations.

Having done that, I get other benefits too. For example, fish (like other shells) has good support for argument completion for well-known commands. The problem is, if you alias such a command, you don't get that completion. With an abbreviation though you do! All you need to do is type the abbreviation, hit space and it'll expand to the underlying command and then the full range of completion can happen.

There's also one last reason why I like abbreviations over aliases, and it's kind of a silly one, but in a good way. It's actually fun to see what you type magically expand as you do things, it makes you look like you can type even faster than you normally can! ;-)

PS: If you've never tried fish before and you're curious, it's easy to try in your browser.