Double parenthesis with and without dollar

Question

Is $(...) the same as (...) in Bash?

Also, is $((...)) the same as ((...))?

Also, is ${...} the sa

Answer 1

Adding to the answer above:

1. [..] is used in conditions or logical expressions. Example:

$ VAR=2
$ if [ $VAR -eq 2 ]

> then
> echo 'yes'
> fi
yes

2. [[...]] offers extended functionality to single square brackets. Particularly, it is useful for =~ operator (used in regular expressions). Example:

$ VAR='some string'
$ if [[ $VAR =~ [a-z] ]]; then
> echo 'is alphabetic'
> fi
is alphabetic

Reference:

https://linuxconfig.org/bash-scripting-parenthesis-explained