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?