Variables

A variable is a name that stores a value, so you can use it later.

fish

set name Obay
echo "hi $name"
# hi Obay

In fish you write set, then the name, then the value. To read it back, put a $ in front.

bash

name=Obay
echo "hi $name"
# hi Obay

In bash you write name=value with no spaces around the =. name = Obay won’t work, because bash thinks you’re running a command called name.

Lists

A variable can also hold several values.

fish

set colors red green blue
echo $colors[2]
# green
count $colors
# 3

In fish, every variable is a list. A normal variable is just a list with one thing in it. Counting starts at 1.

bash

colors=(red green blue)
echo "${colors[1]}"
# green
echo "${#colors[@]}"
# 3

Bash calls these arrays. Counting starts at 0, and the syntax is a bit longer. You’ll mostly see arrays in bigger scripts.

Environment variables

Your shell starts with some variables already set. These are called environment variables, and they’re usually written in capital letters:

echo $HOME    # your home folder
echo $USER    # your username
echo $PATH    # where the shell looks for commands

$PATH is the list of folders where the shell looks for programs. When you type ls, the shell goes through those folders one by one until it finds a program called ls. You’ll use this in later chapters.

fish

To make a variable visible to the programs you run, add -x (for export):

set -x EDITOR nano

That lasts until you close the terminal. To keep it after that, add -U (for universal) as well:

set -Ux EDITOR nano

bash

To make a variable visible to the programs you run, use export:

export EDITOR=nano

That lasts until you close the terminal. To keep it, put the same line in the file ~/.bashrc, which bash runs every time it starts.

Math

Since variables are text, you need a command to do math:

fish

math 2 + 3
# 5
math 10 / 4
# 2.5

bash

echo $(( 2 + 3 ))
# 5
echo $(( 10 / 4 ))
# 2

Bash does math inside $(( )), and only with whole numbers, so 10 / 4 is 2.