bash - Make shopt change local to function

Question

I'm trying to write a bash function that uses nocasematch without changing the callers setting of the option. The function definition is:

is_hello_world() {
  shopt -s nocasematch
  [[ "$1" =~ "hello world" ]] 
}

Before I call it:

$ shopt nocasematch
nocasematch     off

Call it:

$ is_hello_world 'hello world' && echo Yes
Yes
$ is_hello_world 'Hello World' && echo Yes
Yes

As expected, but now nocasematch of the caller has changed:

$ shopt nocasematch
nocasematch     on

Is there any easy way to make the option change local to the function?

I know I can check the return value of shopt -q but that still means the function should remember this and reset it before exit.

Answer 1

The function body can be any compound command, not just a group command ( {} ). Use a sub-shell:

is_hello_world() (
  shopt -s nocasematch
  [[ "$1" =~ "hello world" ]] 
)