title: Zsh Variable Substitution
tags: linux macos zsh variables

## Substrings
Zsh uses the `$var[a,b]` syntax where it extracts the substring from `a` to `b` inclusive (`b` is position, not length like with `substr()`). Use `-1` for the end of the string. Indexing is 1-based, so `$var[1]` is the first
character of `$var` if `$var` is not an array, else it is the first element of the array.
```bash
% name="John"
% echo $name[1,2]
```

## Changing case to upper or lower
Sources: [official docs](https://zsh.sourceforge.io/Intro/intro_12.html)
and [scriptingosx.com](https://scriptingosx.com/2019/12/upper-or-lower-casing-strings-in-bash-and-zsh/)
For zsh
```bash
% name="John Doe"
% echo ${name:l}
john doe
% echo ${name:u}
JOHN DOE

# Capitalise first letter, rest lowercase
% name="jOHN"
% echo "${name[0,1]:u}${name[2,-1]:l}"
John
```

## Arrays
```bash
% a=(hello world mr flibble)
% echo $a[1]
hello
% echo $a[3]
mr
% echo $a[3,4]
mr flibble
% echo $a[-1,-1]
flibble
% echo $a[-2,-1]
mr flibble
% echo $a[-1,-2]
# blank
```