Fish Shell is a unique user-friendly command-line shell for the different operating systems. fish includes some smart features like syntax highlighting, fancy tab completions and autosuggest-as-we-type that just works by default with no configuration required. fish is mostly written in shell script and in C++.
Step 1: Install fish repository in ubuntu
$ sudo apt-add-repository ppa:fish-shell/release-3
Step 2: Update and upgrade repository
$ sudo apt-get update && sudo apt-get upgrade
Step 3: Install fish shell
$ sudo apt-get install fish
Step 4: Make fish shell as default shell
$ sudo chsh -s /usr/local/bin/fish
To get back to bash, use
$ sudo chsh -s 'which bash'