Parentheses in shell programming

Parentheses are used to run a group of commands,

The command enclosed by () indicates to run in the sub-shell without affecting the current shell environment.
The command enclosed by {} indicates that the command is run in the current shell, and the running result will affect the current shell environment.

If the command in braces is to be typed in the same line, there must be a space after the left brace and a semicolon after the last command
{Date; LS; Cd ~;}

Parentheses are not required.
(Date; LS; Cd ~)

[] Indicates the test command. There must be a space behind the brackets on the left and a space before the brackets on the right.
["$1" = 10]

$ (I + 1) is an arithmetic extension in shell programming.