Is double square brackets [[ ]] preferable over single square brackets [ ] in Bash?

Question

A co-worker claimed recently in a code review that the [[ ]] construct is to be preferred over [ ] in constructs like

if [ \"`id -         


        

Answer 1

In a nutshell, [[ is better because it doesn't fork another process. No brackets or a single bracket is slower than a double bracket because it forks another process.