The shebang is used if you run the script directly as an executable file (for example with the command ./script.sh ). In this case it tells the operating system which executable to run. It's not required and has no effect if you for example write bash ./script.sh or source the script.

What is a shebang used for?

shebang is used to tell the kernel which interpreter should be used to run the commands present in the file. When we run a file starting with #! , the kernel opens the file and takes the contents written right after the #! until the end of the line.

Why do people write shebang?

The shebang is a directive to the loader to use the program which is specified after the #! as the interpreter for the file in question when you try to execute it. So, if you try to run a file called foo.sh which has #!/bin/bash at the top, the actual command that runs is /bin/bash foo.sh .