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Directory and File Commands

Linux Tips by Burleson Consulting

In Linux, all entities are described in files so learning how to examine and manipulate them is a good place to start.  End users are most familiar with files containing data that they work with on a daily basis.  Files can also include such things as end-user programs in addition to operating system programs, program control parameters, hardware device descriptions, and system status information. 

Files are stored in directories, which are referred to as folders in a GUI environment.  Directories are arranged in a hierarchical tree structure.  Everyday workings within a Linux environment will require that the user understand where their files are stored, how to navigate through the directory tree, and how to manipulate files within the directory structure.

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.

The tree command can be used to display the directory tree from the command line, but the displayed output can be rather cumbersome to decipher.  By default, the tree command starts in the current working directory and creates a graphic display of all child directories and the files in each directory. 

tree.

|-- System.map -> System.map-2.4.9-e.25
|-- System.map-2.4.9-e.25
-- System.map-2.4.9-e.3
|-- boot.b
|-- chain.b
|-- grub
|   |-- device.map
|   |-- e2fs_stage1_5
|   |-- fat_stage1_5
|   |-- ffs_stage1_5
|   |-- grub.conf
|   |-- menu.lst -> ./grub.conf
|   |-- minix_stage1_5
|   |-- reiserfs_stage1_5
|   |-- splash.xpm.gz
|   |-- stage1
|   |-- stage2
|   `-- vstafs_stage1_5
|-- initrd-2.4.9-e.25.img
|-- initrd-2.4.9-e.3.img
|-- kernel.h -> kernel.h-2.4.9
|-- kernel.h-2.4.9
|-- lost+found [error opening dir]
|-- message
|-- module-info -> module-info-2.4.9-e.25
|-- module-info-2.4.9-e.25
|-- module-info-2.4.9-e.3
|-- os2_d.b
|-- vmlinux-2.4.9-e.25
|-- vmlinux-2.4.9-e.3
|-- vmlinuz -> vmlinuz-2.4.9-e.25
|-- vmlinuz-2.4.9-e.25
`-- vmlinuz-2.4.9-e.3

2 directories, 31 files

To limit the display to just directories without the files contained in each directory, the ?d option can be used.  The following is an example of the output from the tree command with and without the ?d option.

 $ tree ?d
.
|-- grub
`-- lost+found [error opening dir]

 
2 directories

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:

Symbol

Displayed Value

 \!

History number of current command

\#

Command number of current command

 \d

Current date

\h 

Host name

\n

Newline

\s

Shell name

\t

Current time

\u

User name

\W

Current working directory

\w

 Current working directory (full path)

Table 4.1: PS1 prompt string values

This is an excerpt from "Easy Linux Commands" by Linux guru Jon Emmons.  You can purchase it for only $19.95 (30%-off) at this link.


 

 

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