The Hidden Power of Unix File Descriptors
File descriptors
In Unix and Unix-like operating systems, a file descriptor is a unique identifier for a file. For instance, /etc/environment is the descriptor that refers to the system-wide configuration file for environment variables. Nothing special, so far.
Regular files, symbolic links, directories
But that’s not all there is to the story. You probably know that besides regular files, file descriptors can also refer to other file types, such as symbolic links and directories.
Symbolic links are links to files that behave just like the file itself, but you can move them around, make copies of them and remove them, without affecting the original file. And if you modify the contents of either the original or a symbolic link, both are kept in sync. This is very handy, for instance, if you want to share files across different users or for file management. On my machine, for instance, I like to keep my work projects close at hand withhome/tdeneire/work, but this is actually just a symbolic link to /home/tdeneire/backup/Dropbox/projects/work (which is much less manageable) so that the whole directory is automatically backed up to the cloud…
This example of a symbolic link to a directory shows how, in Unix, directories are a file type…
