Guide to Linux Installation and Administration, 2e1 Chapter 6 Using the Shell and Text Files

Guide to Linux Installation and Administration, 2e 1

Chapter 6

Using the Shell and Text Files


Objectives

In this chapter, you will:

• Describe how a Linux shell operates

• Customize your shell environment

• Use common text editors to create or modify text files

• Describe popular text-processing methods and tools used on Linux


Understanding the Shell

• Command interpreter: program that accepts input from the keyboard and launches commands or otherwise controls the computer system

• Linux command interpreter is called the shell

• The shell is only loaded when a user logs in at a text mode login prompt

• Different types of shells are available for Linux

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The Shell Prompt

• Shell prompt: set of words or characters indicating that the shell is ready for commands

• The default shell prompt includes four components:– The user account name

– The hostname

– The last part of the full directory path

– A prompt character




A Standard Shell Prompt


The Functions of a Shell

• A shell’s primary purpose is to launch programs• A Linux shell gives users the ability to write

scripts that the shell can execute• The shell has many built-in features to work with

files and commands on a Linux system




Different Types of Shells


Different Types of Shells


Entering Commands

• Modern shells include features designed to simplify the process of entering commands and command parameters:– Tab completion

– History feature




Using Tab Completion

• Tab completion is a shell feature that lets you enter part of a file or directory name, press the Tab key, and have the shell fill in the remainder of the name

• Using tab completion makes it easier to enter long or complex directory paths and filenames




Using the History Feature

• Command history: records each command that you enter at the shell prompt

• History list: recently entered commands• To locate a previously executed command

– Use the history number

– Use the beginning of a command

– Search the history list




The Shell Start-up Process

• The profile scripts are executed when a user logs into a Linux system

• Additional scripts are executed when a user starts a shell

• The /etc/profile script contains configuration information that applies to every user on the system




A Typical Start-up Script


Customizing the Shell

• You can customize the Linux environment with the following methods:– Use aliases

– Use symbolic links

– Use environment variables




Using Aliases

• Alias: string of characters that is substituted for another string of characters at the shell prompt

• The alias command lets you define an alias for text you enter at a shell prompt

• General format of the alias command:

alias<string entered>=<string substituted by the shell>




Symbolic Links

• Symbolic link– File that refers to another file or directory, rather

than containing data itself

– Used when the same data must be accessed from two locations in the directory structure, or by two different names

– Commonly used in directories such as /lib and /usr/lib

• To create a symbolic link, use the ln command with the -s option




A Symbolic Link


Viewing a Symbolic Link


Environment Variables

• Environment variables are settings, or values, available to any program launched by a user

• Each environment variable is assigned a value• Set command: displays a list of all environment

variables defined in your current environment• To see the value of an environment variable,

execute echo followed by the environment variable name preceded by a dollar sign

• The export command makes an environment variable available to other programs launched from that environment




Using Text Editors

• Linux supports numerous text editors• Linux system administrator can modify

configuration files using any text editor• Files that use a markup language can be created

in any text editor• You can filter text files within some text editors




The Variety of Linux Text Editors

• Graphical text editors are included on modern Linux desktops, such as– gedit in Gnome

– kedit and kate in KDE

• Widely used text-mode editors:– vi

– emacs

– pico

– joe




The pico Text Editor


Using the vi Editor

• vi is a modal editor – keystrokes are interpreted differently depending on the mode you are working in

• vi has several modes:– Command mode

– Insert mode

– Replace mode




Using the vi Editor


vi Commands to Enter Insert or Replace Mode


Additional vi Commands


Text Processing

• There are two methods to create formatted documents:– Graphical, or WYSIWYG (what-you-see-is-what-

you-get)

– Rely on markup languages to define special codes that format documents




Markup Languages

• Widely used markup languages in the Unix and Linux world:– HTML (hypertext markup language)

– TeX – a document-processing system with two popular versions: LaTeX and TeTeX

– roff codes for online documents




An HTML Document in vi


Controlling Fonts

• The X Window System is installed with many different fonts

• xfontsel graphical program is used to review and select fonts

• Both Gnome and KDE provide a standard font selection dialog box

• Fonts are managed in X using the xfs font server• New fonts can be added to the Linux system any

time




The xfontsel Program


The Font Selector Dialog Box in Gnome


Manipulating Text Files

• Filtering is the process of adding, removing, or altering data in the text file based on complex rules or patterns

• sort command: sorts all of the lines in a text file, writing them out in alphabetical order

• sed command: processes each line in a text file according to a series of command-line options

• awk and perl programming languages can be used to create scripts for filtering text files




Linux Text-filtering Commands


Summary

• Linux shell: program that launches other programs and works with files in Linux

• Modern shells include features designed to simplify the process of entering commands - tab completion and history

• Aliases within a shell cause the shell to replace text on a command-line entry with different text before trying to execute the command

• Environment variables store values that any program can access


Summary

• Linux supports text editors, such as vi • Linux programs format text using a WYSIWYG

display or markup languages such as LaTeX and roff use codes

• Fonts are managed in X Windows System using a font server

• Gnome and KDE provide a dialog box to select the font for graphical programs

• Filtering text files can be done within some text editors or using different command-line utilities

Documents

Guide to Linux Installation and Administration, 2e1 Chapter 6 Using the Shell and Text Files