Explain fish code

What this fish sample shows

variables

fish sets variables with set, not NAME=value. -g makes one global and -x exports it to the programs fish starts, so set -gx EDITOR nano gave EDITOR=nano. set -g fish_greeting with no value empties the greeting, so a new terminal opens without one.

PATH

fish_add_path ~/bin puts ~/bin first on the PATH and leaves it alone if it's already there: after running it again and re-reading the file, ~/bin was still listed once. command -v hello then found the hello script in ~/bin.

abbreviations and aliases

An abbreviation is expanded on the command line as you type, so the full git status --short lands in your history. alias in fish writes a small function: type ll showed function ll --wraps='ls -lah'. fish already ships an ll of its own, ls -lh, and the alias replaces it.

functions and status

function ... end defines a command, and $argv holds its arguments, starting at 1: mkcd a/b made both folders and moved into them. ; and runs the next command only if the one before it worked. if status is-interactive keeps the shortcuts to terminals you type into; the rest of the file runs for every fish, so a fish -c script still had EDITOR and mkcd.

Good to know

• Run with fish 4.8.1 on a test home folder, so nothing touched a real config.
• Some bash habits work in fish 4.8.1: export FOO=bar, $(echo hi) and true && echo ok all ran. A bash if [ 1 = 1 ]; then echo yes; fi didn't: fish stopped with Missing end to balance this if statement, because fish ends an if with end.
• fish doesn't split variables on spaces: with set f "my file.txt", count $f printed 1. Lists start at 1, and $l[-1] is the last item.

Watch out: Abbreviations exist only while you type. In a fish script, abbr --add gs git status --short followed by gs didn't run git: it ran the real gs command, which on the test machine was GPL Ghostscript 10.07.1. Write the full command, or a function, in scripts.