Replace string with string in bash

Replacing strings in bash is something I do on a regular basis.

It is quite easy, but I tend to forget the exact syntax, so this is here for me to look it up every know and then.

How to replace a string within a string in pure bash:

#!/bin/bash
firstString="I love Suzi and Marry"
secondString="Sara"
echo "${firstString/Suzi/$secondString}"