Explain: #!/bin/bash - or #!/bin/bash -- In A Shell Script

Q. I know #!/bin/bash is shebang line. But, I noticed a few shell script shebang line ends with a single dash ( #!/bin/bash – ) or double dash ( #!/bin/bash — ). Can you explains me purpose of such shebang line?

A. A – or — signals the end of options and disables further option processing i.e. bash will not accept any of its option. Any arguments after the — are treated as filenames and arguments. An argument of – is equivalent to –. This is done to improve script security. Some user may perform setuid based script root spoofing. To avoid interpreter spoofing you need to add — to #!/bin/bash. This is rare but possible attack.