How to list all distinct extensions of tracked files in a git repository?

I'd like to know all distinct extensions of files tracked by git in a given repo, in order to create appropriate .gitattributes file.

Example output expected:

bat
gitignore
gradle
html
jar
java
js
json
md
png
properties
py
svg
webp
xml
yml

What command can I use for that?

Solution

git ls-tree -r HEAD --name-only | perl -ne 'print $1 if m/\.([^.\/]+)$/' | sort -u

When you declare it as an alias, you have to escape $1:

alias gitFileExtensions="git ls-tree -r HEAD --name-only | perl -ne 'print \$1 if m/\.([^.\/]+)$/' | sort -u"

This is better than naive find, because:

it excludes untracked (gitignored) files
it excludes .git directory which contains usually hundreds/thousands of files and hence slows down the search