What does a file descriptor uniquely represent in an operating system?

A file descriptor uniquely represents an open file in an operating system. When a file is opened, whether it be a regular file, a directory, or a device file, the operating system creates a file descriptor—a small integer value that acts as a handle for that open file. This integer is used by the operating system and applications to refer to the file for subsequent read, write, and control operations.

The concept of file descriptors is crucial in systems programming because it allows processes to interact with files in an efficient manner. Each time a file is opened, a new file descriptor is generated, ensuring that even if multiple files are open at the same time, they can be managed independently through their respective descriptors.

When a process wants to perform actions on files or devices, it uses these file descriptors rather than directly interacting with the file names or paths, abstracting away the details of how the operating system manages files under the hood. This mechanism ensures safe and efficient file handling in a multitasking environment.