$() vs () bash

$() vs `` bash

$() or `` is called command subsitution

They are the same. Command subsitution allows the output of a command to 
replace the command identifier.

() vs {} bash

() 
- Placing a list of commands between parentheses causes a subshell environment
to be created, and each of the commands in list to be executed in that subshell.
Since the list is executed in a subshell, variable assignments do not remain 
in effect after the subshell completes.

{}
- Placing a list of commands between curly braces causes the list to be executed
in the current shell context. No subshell is created. The semicolon (or newline)
following list is required.

$() vs () bash

$(cmd) substitutes the result of cmd as a string, whereas (cmd; cmd) run a list of commands in a subprocess.

If you want to put the output of one or more commands into a variable use the $( cmd ) form.

However if you want to run a number of commands and treat them as a single unit use the () form.

The latter is useful when you want to run a set of commands in the background.

Source: stackoverflow.com

Similar codes

1 vote174 views2 answers
Htop
Shell/Bash
0 vote217 views2 answers
Ubuntu commands
Shell/Bash
22 votes222 views1 answer
Xcode-selec not working
Shell/Bash
2 votes172 views1 answer
How to unzip a file using the cmd?
Shell/Bash
0 vote197 views1 answer
Zh-Hans publish
Shell/Bash
197 votes499 views6 answers
Git new branch from current
Shell/Bash
-2 votes160 views1 answer
Dockerfile run app cmd
Shell/Bash
45 votes284 views6 answers
Git stash docs
Shell/Bash
2 votes165 views1 answer
Find text pattern in file linux
Shell/Bash
1 vote185 views1 answer
Echo variable referenced in variable
Shell/Bash