Fish Shell

Jun 24, 2019
Oct 15, 2019

process substitution: is a form of inter-process communication that allows the input or output of a command to appear as a file.; The command is substituted in-line, where a file name would normally occur, by the command shell.; echo (cat README.md | psub)

How to test if a variable (env) is set or not ¹

set -q var (note the missing “$” - this uses the variable name) can be used to check if a variable has been set.
set -q var[1] can be used to check whether the first element of a variable has been assigned (i.e. whether it is non-empty as a list).
use fish test function
1. When using a variable as an argument for a test operator you should almost always enclose it in double-quotes².

Input/Output (IO) redirection

FD: file descriptors

The reason for providing for two output file descriptors is to allow separation of errors and warnings from regular program output.

IO stream	Symbol
stdinput	<0
stdout	1>
stderr	2>

To not overwrite clobber an existing file, write >?DESTINATION or 2>?DESTINATION


    # >&2 redirection shortcut for 1>&2.
    date 1>&2

redirect stdout (1) to referenced file descriptor (&) stderr (2)
stdout redirection
stderr redirection to referenced file descriptor

How to set terminal text color?

set_color

fish shell webUI

How to run a string

use eval

Fish scripting patterns

variables scopes set vs set -l and accessibility
How to use colors in terminal text
conditional if a variable is set
conditional test -gt
Append to an array
previous command echo $status code
tee /dev/tty
and and or operator in if conditions using begin-end syntax

So there are three options:

Command Substitution: $(...)
Process Substitution: <(...)
zsh-Flavored Process Substitution: =(...)

File Descriptor in fish

What happen when you start the shell

loads configuration
1. system wide /etc/fish/config.fish
2. user specific $HOME/.config/config.fish
prepares and makes available all Environment variables. unlike other shells no subshells³
useful command-line parameters for fish, aka subshell in other shells
1. --inint-command=USR_CMD
2. --command=USR_CMD

shell function to fish escape characters bind

there are special bind functions available

fish_key_reader to stdout input received by terminal

# sane navigation
echo $dirprev; echo $dirnext;
prevd --list <index>

fish_key_reader --continuous
bind \e prevd
bind \c] nextd

# list of all bind functions
bind --function-names

Keybinding	fish escape sequence
`ALT` + `w`	\ew
`CTRL` + `x`	\cx

Note that Alt-based key bindings are case sensitive and Control-based
key bindings are not. This is a constraint of text-based terminals,
not fish.<br>

Every program on your computer can be used as a command in fish

the default keybinding

   bind '' self-insert

reading user inputs and then check then with switch structure

read line1
read --prompt-str='Enter line2 : ' line2
echo $line1 then $line2

Completion and shell suggestions

avoid running dangerous commands dont have to look at man pages or help again and again, all at the ease of TAB key

git complition
Look for fish completion search path from fish_complete_path variable

How to write personal man page and install it on any linux system?

linux-unix-creating-a-manpage
ToDo - add completion for bat

command substitution: The output of a series of commands can be used as the parameters to another command
piping: stdout of a program is used as stdin for other
brace expansion: mv *.{c,h} src/ echo {good,bad}” apples”
process expansion: echo %self

 ~/D/P/avimehenwal.in   master ±  echo %chrome                                                                                                                                          I 
1424 2579 2607 24354 24363 24374 24404 24409 24631 24738 24791 25016 25067 25076 25093 25105 25120 25520 25610 25652 25908 26961 29077 29097 29109 29126 29154 29173 29186 29210 29227 29250 29280 29296 29313 29333 29349 29365 29387 29402 29421 29438 29455 29477 29489 29503 29517 29541 29559 29584 29598 29612 29775 29787 29799 29813 29842 29857 29879 29901 29918 29931 29949 29971 29991 30003 30020 30040 30065 30077 30092 31487 31509 31562
 ~/D/P/avimehenwal.in   master ±  echo %python3                                                                                                                                         I 
754 23757
 ~/D/P/avimehenwal.in   master ±  echo %python                                                                                                                                          I 
754 23757
 ~/D/P/avimehenwal.in   master ±  echo %code                                                                                                                                            I 
28079 28082 28110 28123 28285 28286 28316 28402 28595 28621 28622 28652 28831
 ~/D/P/avimehenwal.in   master ±                                                                                                                                                        I

Command substitutions
Variable expansions
Process Expansion
Bracket expansion
Pid expansion
Wildcard expansion

Variable expansion

however, an important difference in how variables are expanded when quoted and when unquoted. An unquoted variable expansion will result in a variable number of arguments. For example, if the variable $foo has zero elements or is undefined, the argument $foo will expand to zero elements. If the variable $foo is an array of five elements, the argument $foo will expand to five elements. When quoted, like “$foo”, a variable expansion will always result in exactly one argument.

Debugging

breakpoint -

set -l foo begin set -l foo end will create a second version of $foo inside that block, and return to the other once the block ends.

So, what you need to do is to define it outside of the block and then just change it inside:

How to upgrade fish shell

sudo apt-get install --only-upgrade fish

Update fish completions from MAN pages

fish_update_completions

How to test files and directories in fish shell?

use fish test operator

if test -e /path/filename
    echo "File exists"
end

if test -d /directory/
    echo "Directory exists"
end

how to set environment variables in fish shell?

set --[global|local|universal] --export/x <variable_name>

$LINES: number of lines (or rows) in the current terminal

Fonts and Typography

Nerd Fonts 4.1GB
font with powerline glyphs and zsh/bash/fish theme
Fonts
fc-cache -vf ~/.local/share/fonts/
sudo apt install -y fontforge fontforge-doc/rolling fontforge-extras/rolling python-fontforge/rolling

UTF-chars File

fc-list | grep -i Hack
sudo apt install -y fonts-hack-ttf
echo $TERM $LANG
echo -e '\xe2\x82\xac'  # print euro sign
locale charmap          # ISO-8859-1

wget https://www.cl.cam.ac.uk/~mgk25/ucs/examples/TeX.txt; and cat