【bash】How to solve : Syntax error: "(" unexpected

I wrote some shell scripts and try to execute in docker httpd environment by typing below command

sh sample.sh

then I got this error.

sample.sh: 13: Syntax error: "(" unexpected

Yes I have "(" in line 13 but what's wrong with that? The thing is if you are under Debian environment like Ubuntu, "sh" does not stand for "bash" but "dash" . You can see it by typing as below.

ls -ltra /bin/sh 
lrwxrwxrwx 1 root root 4 Dec  1 00:00 /bin/sh -> dash

Solution. In stead of "sh sample.sh", just use "bash" as below.

bash sample.sh

Then you get what you want without errors no more!