Sharing Files in Linux and Understanding Pathnames
Going Dotty in the Linux Filesystem
Akkana Peck
Wednesday, February 25, 2009 05:05:44 PM
In Navigating
the Filesystem I talked about how pathnames work, the
difference between /home and home, and using ls to see the contents
of a directory. But there are a few more useful
tricks you ought to know about finding your way around in the
filesystem on your disk.
Getting dotty
First, an admission: when you type ls, the system is fibbing to you.
There are a lot of files it's not telling you about -- so-called
"hidden files". To see them, type: ls -a (a in this case
stands for "all").
You'll see a lot of files starting with a period, like .bashrc,
.mozilla and so forth. Most of those are configuration files or
directories used by programs you run. But at the beginning, you'll
also see two curious entries: . and ..
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These two names act like directories -- you can ls them or cd into
them -- but they take you somewhere relative to the directory you're
in.
.. is the most useful: it takes you up one level.
If you're in your home directory, /home/you, and you type
cd ..
you'll end up in /home (type a pwd to make sure).
Another cd .. and you'll be in /, the root directory.
This is particularly useful since you can string them into longer
pathnames. If you're in /usr/bin and you type cd ../lib,
you'll end up in /usr/lib: from /usr/bin, .. means one level up,
or /usr. It may not seem that useful just to get from /usr/bin to
/usr/lib, but just suppose you were in /usr/lib/gimp/2.0/plug-ins
and you wanted to get to /usr/lib/gimp/2.0/scripts. Rather than
typing that whole thing out, just type cd ../scripts
and you're there.
What about the single dot? . means the current directory.
So cd . doesn't do anything; it just leaves you in the
same place you already were.
What good is that? Sounds pretty useless, huh? But it actually does
have uses. For one thing, you can use it for programs like find that
insist on being told where to start. For another, you can use it when
running programs. If you've ever built any programs from source,
you might have seen instructions to type "./configure". That means
"run the program called configure that's in the current directory,
even if there's another program with that name installed somewhere
else."
Even if you don't use the . a lot, it's good to know what it means;
you'll see it when people talk about Linux commands.
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