FISH

The friendly interactive shell.

TL;DR
Configuration
Prompt
Key bindings
Further readings
Sources

TL;DR

# Install the shell.
apt install 'fish'
brew install 'fish'
zypper install 'fish'

# Start `fish` sessions.
fish
fish -Pil

# Set variables.
set 'MyVAR' 'someValue'
set -x 'MyExportedVAR' 'someValue'

# Unset variables.
set -e 'MyVAR'

# Change one's default shell to `fish`.
chsh -s (which fish)      # from `fish`
chsh -s "$(which fish)"   # from `{ba,z}sh`

# Open the web-based configuration interface.
fish_config
fish_config browse

# Process substitution.
# What in BASH or ZSH would be `<(echo …)`.
diff -y -W 200 \
  (aws … --output 'json' | psub) \
  (aws … --output 'json' | psub)

# Math.
math 2 '+' 6
time pulumi pre --parallel (math 2 '*' (nproc))

# Array manipulation.
echo (seq 10)[-1..1]  # -> 10 9 8 7 6 5 4 3 2 1
set array "$array appended_element"

# Define CLI options.
# Use all lines.
set -l opts
set opts $opts (fish_opt -s 'c' -l 'command' --required-val)
set opts $opts (fish_opt -s 'p' -l 'path' --multiple-vals)
argparse $opts -- $argv
or return
echo $_flag_command
echo $_flag_path
echo $argv

# Switch.
switch $animal
  case cat
    echo evil
  case wolf dog human moose dolphin whale
    echo mammal
  case duck goose albatross
    echo bird
  case shark trout stingray
    echo fish
  case '*'
    echo I have no idea what a $animal is
end

For functions defined in files in ~/.config/fish/functions/ to be automatically available, the files need to:

Host a single function each.
Be named as the function they host.

Configuration

Shell configuration file: ~/.config/fish/config.fish.
.fish scripts in ~/.config/fish/conf.d/ are automatically executed before config.fish.

Configuration files are read at startup of every session, whether the shell is interactive and/or login.
Use status --is-interactive and status --is-login to discriminate between interactive/login shells, respectively:

if status --is-login
  fish_add_path ~/bin
end

fish offers a web-based configuration interface. Open it executing fish_config.

Prompt

See Starship or Tide.

Key bindings

# Show all active key bindings.
bind

Key combination	Binding name	Effect
`CTRL` + `k`	`kill-line`	Delete text from the cursor position to the end of the line
`CTRL` + `e`	`end-of-line`	Move the cursor to the end of the line
`CTRL` + `w`	`backward-kill-path-component`	Delete previous word
`CTRL` + `u`	`backward-kill-line`	Delete text from the beginning of the line to the cursor position
`CTRL` + `l`	`clear-screen`	Clear screen

Sources

All the references in the further readings section, plus the following:

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