The #! characters at the beginning of a shell script are called a shebang. They are followed by the path to the interpreter that should be used to execute the script.
In the case of #!/bin/bash, the script should be interpreted by the Bash shell, which is a widely used command-line interpreter for Unix-like operating systems.
The - or -- characters that may appear after the path to the interpreter are optional and are not required to execute the script.
The - character is typically used to pass a single argument to the interpreter. For example, you might use #!/bin/bash -x to run the script with the -x option, which causes the Bash shell to print each command before executing it.
The -- characters are used to indicate the end of the options passed to the interpreter. This is useful if the script itself contains arguments that start with a - character, as it allows the interpreter to distinguish between arguments intended for the interpreter and arguments intended for the script.
For example, consider the following script:
#!/bin/bash -- echo "Hello, world!"
If the -- characters were not present, the Bash shell might interpret the echo command as an option and produce an error. With the -- characters, the Bash shell knows to treat everything after them as arguments to the script, and the script runs correctly.
In general, it is a good idea to include the -- characters in your scripts, as it can help to avoid confusion and ensure that the script is executed as intended.