{ } and ( ), two different ways of grouping commands in shell script.

There are two different ways of grouping commands in unix shell script.

i) ( ) : When we group commands inside ( ), the commands are executed in the subshell, instead of current shell.

ii) { } : When we group commands inside { }, the commands are executed in the current shell.

Let's understand it with the help of an example. In this example, we will try to change the working directory of a shell and verify whether it has been changed or not.

Open shell and type the following command. Assuming that shell's pwd before executing the below command is /

$ { cd /etc/mail ; pwd ; }

The output will be

/etc/mail

This cd command was run on the current shell. If you want to verify, execute pwd again and you will see the same output

$ pwd

/etc/mail

Now, we will execute the same set of commands using ( ). Again assuming that pwd is /etc/mail

$ ( cd .. ; pwd )

The output will be

/etc

This cd command was run on the subshell. If you want to verify, execute pwd and you will see the output

$ pwd

/etc/mail

We can see that pwd of the current shell has not changed.

Note: Always use ; before } if { and } appears on the same line. This is not needed in case of ( ).

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