Some languages (e.g. Perl, Python) are old enough to have been concerned with the 3 character extension limit from MS-DOS: https://en.wikipedia.org/wiki/8.3_filename

I can answer the Rust question. In the ancient era, Rust source code was split into two types of files: .rc files and .rs files. The latter were "Rust source" files, and the former were "Rust crate" files. The crate files were essentially header files; they defined the public interface of the crate by explicitly listing items to be exported from the crate. Eventually explicit export lists were removed (and replaced with visibility modifiers on items themselves), and so there was no reason for .rc files to stick around, and nobody really ever objected to .rs as the now-universal extension for Rust files, since it's still a valid abbreviation.

Probably because the first release was in 1996, so Java never ran on a platform (like DOS) that needed only 3 characters. Originally it only ran on Solaris and Windows 95/NT.

If you think .java is brave, wait until you hear about Mojo's extension: https://en.m.wikipedia.org/wiki/Mojo_(programming_language)

They allow the extension to be the fire emoji

I used to write all my html files with .htm… apparently that went out of fashion.

Edit: I got my htm and html backwards and now comment not sense. Fixed now but obviously the folks below were right / responding to an earlier version.

Possibly the following? It wouldn't 'sound' enough like a file name extension if it was the full name '.rust'

Where the inertia of the history of 3-letter extensions in DOS and the likes is what caused this convention, of course

As a RapidSketch user on my organisations web ratings board working group living in a coastal area affected by soil erosion and with a penchant for DNA modelling, I find Rusts choice of file extension perturbing.

.rust.programming.language would make far more sense than pretending Rust will ever need to work in DOS.

> four characters in its file extension

You are not looking close enough. While Java source code has four characters in its file extension (.java), the output of its bytecode compiler has five characters in its file extension (.class).

There's no abbreviation of Java that isn't weird. These all work well:

perl -> pl

python -> py

rust -> rs

ruby -> rb

javascript > js

But java?

java -> ja? jv? jav?

Clearly Sun should've gone with a different name for the language entirely, I dunno, maybe they could've named it after an oak tree instead:

oak -> ok

Hmm, maybe I could get used to "jv" after all.

Pretty sure the answer is that developers are lazy and want to write fewer characters.

"why use big word when small word do trick" - Kevin Malone

Another brave language is Dart. example.dart

Likely it was not a brave decision - just a decision, with no reason to pivot.

Markdown is .md and .markdown.

No one uses the latter, though.

fewer letters saves valuable developer time

typical java, prioritizing verbosity at the expense of efficiency /s