Swift error "Hashbang line is allowed only in the main file" - swift

Question

I wish to create an interpreted Swift command-line utility. Thus, in Xcode 13.1, I create a new project, and use the template "Command Line Tool". This results in an empty project with a single file, called main.swift.
I want to distribute this command-line utility as a single file, so having the "main.swift" name isn't useful. I rename it to MyCommandlineProject.swift, then add the hashbang line on top, and add code that marks it as being the main file. The contents now look as follows:
#!/usr/bin/swift
import Foundation
#main
struct CLI {
static func main() {
print("Hello, World!")
}
}
Despite the #main annotation, I still get the following compiler error:
Hashbang line is allowed only in the main file
Why?

Answer 1

If you are just writing a script you don't need any of that #main stuff. #main is really only for when you have multiple files that you need to compile into an executable.
For a script, like you are writing, you can just add top level functions and they will get called just as if you were writing in a playground.
#!/usr/bin/swift
import Foundation
print("Hello, World!")
You can execute the script with:
chmod 744 scriptName.swift
./scriptName.swift
Or
swift scriptName.swift
Now if you have multiple files, let's call them First.swift:
import Foundation
#main enum First {
static func main() {
print("First.main")
Second.execute()
}
}
And Second.swift:
import Foundation
enum Second {
static func execute() { print("Second.execute") }
}
You have to prefix your entry point with #main like we did for First. You also have to give it a static main() method.
First you have to compile:
swiftc -o awesome First.swift Second.swift
Then to run:
./awesome