Directory and File Commands

This chapter will introduce the commands needed to manipulate files and directories from the Linux command line.

Directory Structure

As mentioned, Linux stores files in directories (folders) which are arranged in a hierarchical or tree structure.  The highest level directory is called root and is identified by a slash character (/).  All other directories in Linux stem from the root directory.  It is admittedly easier to envision the overall structure of the server?s directories using a GUI interface such as Gnome.  Figure 4.1 is an example GUI display of the directory structure of a Linux server.  The figure indicates that the user is in the /boot directory which contains two subdirectories called /grub and /lost+found displayed as folders and numerous files displayed as icons depending upon file type.

Figure 4.1: GUI display of Linux directory structure

Again, this book is written with the assumption that a GUI environment is not available, and that the user is limited to command line, but if you do have a GUI available it may help you understand the directory structure.

Though tree will give us a quick overview of everything in a directory we are often only concerned with certain directories or files.  Later in this chapter we'll talk about how to examine a more specific subset of a directory.

Directory Commands

Here we'll talk a bit about navigating around the Linux filestructure.

What Directory am I In?

When navigating around in Linux it is very easy to forget what directory you're in.  Don't worry, there's a command to help you find out.

The directory that the user is currently in is referred to as the working directory and can be displayed using the pwd (print working directory) command.  The pwd command displays the absolute path name for the current working directory as demonstrated here:

$ pwd
/home/tclark 

The directory /home/tclarc is an absolute path because it begins with a slash.  Absolute paths will refer to the exact same location no matter who types them or where they type them from because the slash specifies that this path is described from the root directory.  The opposite of an absolute path is a relative path which would refer to a subdirectory of the working directory.  Relative paths cannot begin with slashes.

In order to eliminate the need to frequently issue the pwd command to determine the current working directory, many Linux users choose to display the working directory within the Linux command prompt.  Some Linux administrators even provide this service for their users when they create their Linux accounts.  If a user?s command prompt does not contain the working directory, the command prompt can be modified by changing the prompt string 1 (PS1) shell variable as demonstrated here:

$ PS1="[\u@\h \w]\\$ "
[tclark@appsvr /home/tclark]$

This example of setting the PS1 variable also adds the username (\u) and hostname (\h) to the prompt.  This can be very useful if you frequently connect to different hosts and as different users.

In order to avoid having to modify the prompt at each login, the following line of code can be placed within the appropriate configuration file, such as .bash_profile for the bash shell, within the home directory.  To do this you can use a text editor like vi to add the following line to your .bash_profile file:

$ export PS1="[\u@\h \w]\\$ "

Note: Files that begin with a period will not appear when you list the contents of a directory.  To see these hidden files use the command ls ?a

There are even more options which you can put into your PS1 prompt.  While it's nice to keep your prompt fairly short you may find some of the other options useful.  Table 4.1 contains a list of values that can be displayed within the PS1 and/or PS2 prompt strings: