May 25, 2018

Navigating the Linux Filesystem - page 2

Upside-down Trees

  • February 11, 2009
  • By Akkana Peck

Let's go back to that filesystem in Figure 1, where we'd gotten as far as /home. But you can string together more than one directory in a pathname. You know that /home gets you one level below the root; but if you add another directory, you can refer to useful places like /home/sue. On most systems, that's where the user named sue would have her home directory. So when Sue first logs in, her working directory is her home directory, /home/sue.

Remember I said how important it is whether you start with a slash? Suppose Sue has a directory of her own called "home", where she keeps all the records related to her house. If she's in her home directory and types "ls home", that's very different from "ls /home", as Figure 2 illustrates.

$ ls /home
fred                sue
$ ls home
mortgage.ods        paintcodes.odf        photos
See the difference?

Now let's say, going back to Figure 1, that Sue wants to share a photo of her dog with Fred, who has an account on the same system. All she has to do is tell him the full pathname to the photo /home/sue/Pictures/pets/fido.jpg.

There's a shortcut, though. You can use the tilde character, ~, to refer to home directories. A tilde by itself means your own home directory: if Sue wants to edit the Fido photo in GIMP, she can say gimp ~/Pictures/pets/fido.jpg. The ~ stands for /home/sue in any command Sue types.

When Fred types a ~, though, Linux will look in /home/fred instead. If Sue wants to tell Fred where to find her Fido photo, she should use the slightly longer form "~sue", which means "the home directory of user sue", or /home/sue. So she gives Fred the pathname: ~sue/Pictures/pets/fido.jpg, and Fred can use that from anywhere.

Of course, Fred can't necessarily read Sue's files, and vice versa -- there are ways of protecting your files so no one else can see them. But that's a topic for another day!

Akkana Peck is a freelance programmer whose credits include a tour as a Mozilla developer. She's also the author of Beginning GIMP: From Novice to Professional.

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