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- In this video, we are going
to talk about path names.

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So what is there to know about path names?

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Well, you can specify
your paths in two ways.

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As an absolute path.

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An absolute path contains the full name

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from the root directory to a file.

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An example is /var/log/messages.

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The nice thing about an absolute path

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is that it is very clear
what you are referring to.

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Can't be any doubt about it.

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But sometimes it's too much typing.

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And for that reason,
you might be better off

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using a relative path.

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Relative path is related
to the current directory,

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and it contains the rest that
is needed to get to a file,

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like log/messages, which will work

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if the current directory is set to /var.

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Now in relative paths, you can use dot dot

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for one directory up.

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If the current directory is
/var/cache, for instance,

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../log/messages points to
/var/log/messages file.

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But if I may give you a
tip, use absolute paths

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to avoid confusion.

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Now before I'm going to demonstrate,

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let me make a quick drawing

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so that I can visualize what exactly it is

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that we are going to do.

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In this video, I would like
to visualize these relative

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and absolute path names.

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So let's draw a small directory structure.

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Start with the root directory.

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In the root directory, we have etc,

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we have tmp,

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and in tmp we have data.

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Okay, so let's imagine that
in etc, we have this file,

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and the name of this file is passwd.

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And in tmp, we have this file,

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and the name of this file is hosts

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because we copied it over here.

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Now just imagine that we are currently

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in the data directory.

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The data directory, represented by a dot.

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The dot is the current directory.

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And I want to copy this
file up to this location.

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And I'm right here.

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Then what can we do?

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Well, we can use these relative file names

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and use a command like cp dot dot.

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If you use dot dot, then it brings us up

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from the data directory
to the tmp directory

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as our current directory.

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And if I want to use relative
file names to copy it,

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I need to go up one more level.

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So another dot dot, then I
get into the root directory,

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and then I can specify /etc/passwd to dot.

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But hey, is that the most
accurate way of doing it?

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Well, I don't think
so, because in this way

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you probably would be better
off using absolute file names.

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I mean, what's the sense
if you go all the way down

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to the root directory anyway?

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It would make sense if you want
to copy over the file hosts

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to the current directory.

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In that case, you can use
cp.. to go up one level,

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that brings you here.

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Then you can refer to the file hosts,

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and then you can copy
it to the dot directory.

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And that's a little
demo of how you can work

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with these absolute and
relative file names.

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Let me show you what this
looks like on a computer.

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All right, I am going to
create the directory data.

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Notice that this is a relative path.

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I'm in the tmp directory,
and I'm creating data.

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That will create a subdirectory.

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And I am going to copy /etc/hosts to dot

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so that in the data
directory we have /etc/hosts.

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And I'm going to copy
/etc/passwd to /data.

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Is that what I want?

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No, because I want to create
it to the subdirectory

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in this tmp directory.

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So I need a relative path,
and this is the relative path.

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Now I'm going in the data directory,

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and in the data directory I see my passwd.

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Pwd might be convenient as well.

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That is where you can see
what exactly is going on.

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So if I use cp passwd to dot dot,

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can you guess what is going to happen?

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I'm going to copy passwd to one level up.

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And if I want to verify, I'm using ls..,

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and ls.. is showing a lot of stuff,

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including this data directory right here,

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and this passwd directory right here.

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And that is how you use absolute
and relative path names.