Suppose there is a file which is being executed by someone. Is there a way to return the username of whoever is using that file?

implement the logic within the code itself,

to call getlogin function to dump the user name (currently executing to some log file )

this will not take care of sudo users

You could also use the fuser command for this.

Thanks for your reply. Now all I have to do is figure out how to use getlogin()

On a lot of systems where fuser is not available lsof will work.

By execute you mean "open" by another process, right? Or are you talking about locking files -- stopping your process from opening the file when it's already open?

The answers we gave are shell commands. Why do you need getlogin()?

I'm a complete newbie at UNIX. I have an exercise to do where I have to find the username of someone executing a script and print it to another file. I was sort of hoping for a command like finger, where you put in a script name instead of a person, to find out who is using it.