brew cask install kdiff3
Error: Cask 'kdiff3' is unavailable: No Cask with this name exists.
brew install kdiff3
Error: No available formula with the name "kdiff3"
==> Searching for a previously deleted formula (in the last month)...
Warning: homebrew/core is shallow clone. To get complete history run:
git -C "$(brew --repo homebrew/core)" fetch --unshallow
Error: No previously deleted formula found.
==> Searching for similarly named formulae...
Error: No similarly named formulae found.
==> Searching taps...
==> Searching taps on GitHub...
Error: No formulae found in taps.
brew search kdiff3
No formula or cask found for "kdiff3".
Closed pull requests:
tap_migrations: remove kdiff3 (https://github.com/Homebrew/homebrew-core/pull/43798)
Delete kdiff3.rb (https://github.com/Homebrew/homebrew-cask/pull/67726)
p4v 18.3-1719707: Add CLI-accessible commands to work with Git out of the box (https://github.com/Homebrew/homebrew-cask/pull/54957)
Update kdiff3 to 0.9.98 (https://github.com/Homebrew/homebrew-cask/pull/31404)
Update kdiff3 - add shimscript (https://github.com/Homebrew/homebrew-cask/pull/35967)
Secure URLs (https://github.com/Homebrew/homebrew-cask/pull/52975)
kdiff3 migrated to cask (https://github.com/Homebrew/homebrew-core/pull/3335)
kdiff3 0.9.98 (https://github.com/Homebrew/legacy-homebrew/pull/31147)
Added formula kdiff3 (https://github.com/Homebrew/legacy-homebrew/pull/5724)
Update kdiff3 to 0.9.97 (https://github.com/Homebrew/legacy-homebrew/pull/14268)
diffpdf: Bump to 2.1.3 (https://github.com/Homebrew/legacy-homebrew/pull/24912)
Doctor: suggest stashing untracked files rather than deleting (https://github.com/Homebrew/legacy-homebrew/pull/15837)
Upgrade kdiff3 to 0.9.98 (https://github.com/Homebrew/homebrew-cask/pull/5231)
Add binary link to kdiff3 (https://github.com/Homebrew/homebrew-cask/pull/3476)
Add kdiff3.app (https://github.com/Homebrew/homebrew-cask/pull/1847)
bugfix: kdiff3 cask name incorrect (https://github.com/Homebrew/homebrew-cask/pull/1990)
Create kdiff3 v0.9.97 cask (https://github.com/Homebrew/homebrew-cask/pull/1292)
New Cask Kdiff3 v0.9.97 (https://github.com/Homebrew/homebrew-cask/pull/1287)
More efficient listing of installed Casks (https://github.com/Homebrew/homebrew-cask/pull/1778)
brew --version
Homebrew 2.1.16
Homebrew/homebrew-core (git revision 2a800; last commit 2019-11-20)
Homebrew/homebrew-cask (git revision 40638; last commit 2019-11-20)
So how to install kdiff3 using brew on mac os?
kdiff3 was removed from Homebrew’s packages in August 2019 because its last compatible version is five years old. If you really want to install it, you can checkout the formula (package) file in the GitHub repo from just before its removal. You can either copy the file locally or directly use the URL:
brew cask install https://raw.githubusercontent.com/Homebrew/homebrew-cask/6a96e5ea44803e52a43c0c89242390f75d1581ab/Casks/kdiff3.rb