Welcome to Linux Knowledge Base and Tutorial
"The place where you learn linux"
Let The Music Play: Join EFF Today

 Create an AccountHome | Submit News | Your Account  

Tutorial Menu
Linux Tutorial Home
Table of Contents
Up to --> Linux Tutorial

· Shells and Utilities
· The Shell
· The Search Path
· Directory Paths
· Shell Variables
· Permissions
· Regular Expressions and Metacharacters
· Quotes
· Pipes and Redirection
· Interpreting the Command
· Different Kinds of Shells
· Command Line Editing
· Functions
· Job Control
· Aliases
· A Few More Constructs
· The C-Shell
· Commonly Used Utilities
· Looking for Files
· Looking Through Files
· Basic Shell Scripting
· Managing Scripts
· Shell Odds and Ends

Man Pages
Linux Topics
Test Your Knowledge

Site Menu
Site Map
Copyright Info
Terms of Use
Privacy Info
Masthead / Impressum
Your Account

Private Messages

News Archive
Submit News
User Articles
Web Links


The Web

Who's Online
There are currently, 134 guest(s) and 0 member(s) that are online.

You are an Anonymous user. You can register for free by clicking here

Linux Tutorial - Shells and Utilities - Directory Paths
  The Search Path ---- Shell Variables  

Directory Paths

As we discussed in the section on the seach path, you can often start programs simply by inputting their name, provided they lie in your search path. You could also start a program by referencing it through a relative path, the path in relation to your current working directory. To understand the syntax of relative paths, we need to backtrack a moment. As I mentioned, you can refer to any file or directory by specifying the path to that directory. Because they have special significance, there is a way of referring to either your current directory or its parent directory. The current directory is referenced by "." and its parent by ".." (often referred to in conversation as "dot" and "dot-dot").

Because directories are separated from files and other directories by a /, a file in the current directory could be referenced as ./file_name and a file in the parent directory would be referenced as ../file_name. You can reference the parent of the parent by just tacking on another ../, and then continue on to the root directory if you want. So the file ../../file_name is in a directory two levels up from your current directory. This slash (/) is referred to as a forward slash, as compared to a back-slash (\), which is used in DOS to separate path components.

When interpreting your command line, the shell interprets everything up to the last / as a directory name. If we were in the root (upper-most) directory, we could access date in one of several ways. The first two, date and /bin/date, we already know about. Knowing that ./ refers to the current directory means that we could also get to it like this: ./bin/date. This is saying relative to our current directory (./), look in the bin subdirectory for the command date. If we were in the /bin directory, we could start the command like this: ./date. This is useful when the command you want to execute is in your current directory, but the directory is not in your path. (More on this in a moment.)

We can also get the same results from the root directory by starting the command like this: bin/date. If there is a ./ at the beginning, it knows that everything is relative to the current directory. If the command contains only a /, the system knows that everything is relative to the root directory. If no slash is at the beginning, the system searches until it gets to the end of the command or encounters a slash whichever comes first. If there is a slash there (as in our example), it translates this to be a subdirectory of the current directory. So executing the command bin/date is translated the same as ./bin/date.

Let's now assume that we are in our home directory, /home/jimmo (for example). We can obviously access the date command simply as date because it's in our path. However, to access it by a relative path, we could say ../../bin/date. The first ../ moves up one level into /home. The second ../ moves up another level to /. From there, we look in the subdirectory bin for the command date. Keep in mind that throughout this whole process, our current directory does not change. We are still in /home/jimmo.

Searching your path is only done for commands. If we were to enter vi file_name (vi is a text editor) and there was no file called file_name in our current directory, vi would start editing a new file. If we had a subdirectory called text where file_name was, we would have to access it either as vi ./text/file_name or vi text/file_name. Of course, we could access it with the absolute path of vi /home/jimmo/text/file_name.

When you input the path yourself (either a command or a file) The shell interprets each component of a pathname before passing it to the appropriate command. This allows you to come up with some pretty convoluted pathnames if you so choose. For example:

cd /home/jimmo/data/../bin/../../chuck/letters

This example would be interpreted as first changing into the directory /home/jimmo/data/, moving back up to the parent directory (..), then into the subdirectory bin, back into the parent and its parent (../../) and then into the subdirectory chuck/letters. Although this is a pretty contrived example, I know many software packages that rely on relative paths and end up with directory references similar to this example.

Current directory Target directory Relative path Absolute path
/data/home/jimmo/letter /data/home/jimmo/letter/dave ./dave or dave /data/home/jimmo/letter/dave
/data/home/jimmo/letter /data/home/jimmo ../ /data/home/jimmo
/data/home/jimmo/letter /data/home/ ../.. /data/home
/data/home/jimmo/letter /tmp ../../../../tmp /tmp

 Previous Page
The Search Path
  Back to Top
Table of Contents
Next Page 
Shell Variables


Test Your Knowledge

User Comments:

You can only add comments if you are logged in.

Copyright 2002-2009 by James Mohr. Licensed under modified GNU Free Documentation License (Portions of this material originally published by Prentice Hall, Pearson Education, Inc). See here for details. All rights reserved.



Security Code
Security Code
Type Security Code

Don't have an account yet? You can create one. As a registered user you have some advantages like theme manager, comments configuration and post comments with your name.

Help if you can!

Amazon Wish List

Did You Know?
You can get all the latest Site and Linux news by checking out our news page.


Tell a Friend About Us

Bookmark and Share

Web site powered by PHP-Nuke

Is this information useful? At the very least you can help by spreading the word to your favorite newsgroups, mailing lists and forums.
All logos and trademarks in this site are property of their respective owner. The comments are property of their posters. Articles are the property of their respective owners. Unless otherwise stated in the body of the article, article content (C) 1994-2013 by James Mohr. All rights reserved. The stylized page/paper, as well as the terms "The Linux Tutorial", "The Linux Server Tutorial", "The Linux Knowledge Base and Tutorial" and "The place where you learn Linux" are service marks of James Mohr. All rights reserved.
The Linux Knowledge Base and Tutorial may contain links to sites on the Internet, which are owned and operated by third parties. The Linux Tutorial is not responsible for the content of any such third-party site. By viewing/utilizing this web site, you have agreed to our disclaimer, terms of use and privacy policy. Use of automated download software ("harvesters") such as wget, httrack, etc. causes the site to quickly exceed its bandwidth limitation and are therefore expressly prohibited. For more details on this, take a look here

PHP-Nuke Copyright © 2004 by Francisco Burzi. This is free software, and you may redistribute it under the GPL. PHP-Nuke comes with absolutely no warranty, for details, see the license.
Page Generation: 0.10 Seconds