Fishing shells

Posted by R4nd0m 6uy on Mon 26 December 2016

I have been used to bash for years and always thought it was very good but after trying other alternatives I found out that there are more efficient ways to use the command line.

I would like to present here one of my favorite interpreter that is the fish shell. Fish stands for Friendly Interactive Shell and is yet another command line interpreter. Its goal is to be user friendly while being fast.

The major difference with other standards command line interpreters, is that fish is not POSIX and has some subtle differences. People behind fish think POSIX is not adapted for modern usage and decided to not follow it to invent a better, less error prone and more user friendly syntax.

To make the switch less painful, I will try to show the majors difference between the well known bash and give some tips on how to customize it.

Installation

You can install fish shell from the source but it is recommended to use your favorite package manager:

# .deb
apt-get install fish

# .rpm
yum install fish

# Arch
pacman -S fish

# Gentoo
emerge fish

# Void
xbps-install fish-shell

# Other I forgot
# Read the fine manual :)

Starting fish

On your usual shell prompt, you can simply type:

fish

If after some tries your are happy with it, you can set it as default by editing the /etc/passwd manually or by using the chsh command:

chsh -s /usr/bin/fish <your-username>

Common usages

Here is a list useful daily tasks but using the fish syntax.

  • Return code

$? doesn't exist, the status variable is what you are looking for:

fish$ true ; echo $status 
0
fish$ false ; echo $status 
1
  • ;and, ;or

People from fish uses the and/or keyword instead of &&/||

fish$ true ; and echo sucess!
sucess!
fish$ false ; or echo failed!
failed!
  • Variables

When you want to export variables with bash, you would use the export and = sign. Don't add any space in between otherwise it will not work! Lists are not well supported either.

With fish shell, the set built-in is used to declare variables command. With the -x parameter, the variabled is exported. fish supports lists very well and can be declared by using space between each element:

fish$ set -x PATH $PATH $HOME/bin /opt/toolchain/bin
fish$ echo $PATH
/usr/local/bin /bin /usr/bin /home/random/bin/ /opt/toolchain/bin
fish$ set -x ARCH arm
fish$ make menuconfig

More information about list can be found further.

  • Command substitution

Under bash, my favorite flavor is using $(...) but think fish guys think that the $ character is confusing as it is already used for variable expansion, and is consequently not used:

$ echo My usernmae is (whoami)
My usernmae is random
  • Flow control

With fish, you have to use the end keyword that is common for every flow control mechanism unlike done, fi, esac with other shells. Also where fish adds a touch of user friendliness is that it takes care of all the indentation and coloring:

fish$ while true
          uptime
          sleep 1
      end

Another if statement example:

$fish if true
          echo All good
      end
All good
  • Functions

When using a function, parameters are stored in the argv list:

fish$ function hello
          echo Hello $argv[1]
      end
fish$ hello
Hello

fish$ hello world
Hello world

I love the index range expansion feature!

fish$ function hello
          echo Hello $argv[1..-1]
      end
fish$ hello tux world everyone
Hello tux world everyone

Or if you want to say hello to everyone more personnaly:

fish$ function hello
          for who in $argv[1..-1]
              echo Hello $who
          end
      end
fish$ hello tux world everyone
Hello tux
Hello world
Hello everyone
  • time command

It is sometime interesting to know how long it takes to run a command and time built-in bash implementation does the trick very well. In fish, there is no time command but the duration is stored in a variable:

fish$ sleep 1
fish$ echo $CMD_DURATION 
1006

You could implement the time function yourself but you can also use some fish scripts from the communauty. fish_command_timer is my favoriyte, simply clone the repository and source the required file:

fish$ git clone https://github.com/jichu4n/fish-command-timer.git
fish$ . ./fish-command-timer/fish_command_timer.fish
fish$ ls
fish-command-timer/
                                                  [ 0s101 | Dec 09 04:19PM ]

To make this permanent, you can add this your the fish configuration as explained later.

Customization

Of course, fish is highly configurable but again, differs a bit from other shells.

  • .bashrc

If you are looking for something similar to the .bashrc file, you can edit or create the .config/fish/config.fish. Here is for example how mine looks like:

set fish_greeting (uptime)
. /home/random/sources/fish-command-timer/fish_command_timer.fish
  • Prompt

Unlike the PS1 variable, the fish prompt is defined in the fish_prompt function:

fish$ function fish_prompt
          echo -n (whoami)@(cat /etc/hostname)\$" "
      end
random@random-notebook$
  • GIT prompt

Fish is able to show the git branch and repository status on the prompt. Just enable some built-in configurations by adding this in the fish configuration:

set __fish_git_prompt_showdirtystate 'yes'
set __fish_git_prompt_showstashstate 'yes'
set __fish_git_prompt_showuntrackedfiles 'yes'
set __fish_git_prompt_showupstream 'yes'
set __fish_git_prompt_color_branch yellow
set __fish_git_prompt_color_upstream_ahead green
set __fish_git_prompt_color_upstream_behind red

This will change your prompt as follow when inside a git repository:

fish (master) ➞
  • Oh my fish

omf is a repository containing different skins for fish. Everyone is welcome to use it and share his themes. Make sure you have a decent version of fish to have a better user exeprience, unfortunately it doesn't work well on older LTS distriubtions.

Here is how you can install it and user my favorite theme:

fish$ curl -L http://get.oh-my.fish | fish
# ...
fish$ omf install fisk
Installing theme fisk
✔ theme fisk successfully installed.
[0] random@random-notebook ~ ➞

For forther information check the official git repository and the list of available themes

This would probably remind oh my zsh for the zshish!

Common shortcuts

Luckily some shortcuts you learned from bash are also available within fish. Here is the list of the one I use the most frequently:

  • TAB: Enable autocompletion for almost everything :p
  • CTRL+f: Accept fish autosuggestion
  • CTRL+e: Go to the end of the command
  • CTRL+a: Go to the beginning of the command (Anfang in German?)
  • CTRL+p | up arrow : Go to the previous in history
  • CTRL+n | down arrow: Go to the next in history
  • < pattern > CTRL+p|CTRL+n: Look for < pattern > in hostory

Conclusion

Fish has a very nice out of the box configuration and most people will be very happy with it! If you like it and think it could improve your productivity, do not hesitate to have a deeper look at the introduction page and at the documentation for advanced usage.

It has the huge drawback that it is not POSIX but this is OK when using it only in interactive mode. Unfortunately I haven't written many fischripts and would be interesting to see if it really brings much performance improvement.

zsh is a nice alternative, it is very user friendly while respecting the standards. Those who spent a lot of time customizing their zsh will prefer sticking with it but fish worth having a look for your own culture!

tags: shell, tutorial, linux