Using the Shell and Text Files

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Chapter 6

• Using the Shell and Text Files

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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

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Understanding the Shell
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• 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
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• 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

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A Standard Shell Prompt
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The Functions of a Shell
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• A shells 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

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Different Types of Shells
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Different Types of Shells
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Entering Commands
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• Modern shells include features designed to
  simplify the process of entering commands and
  command parameters
• Tab completion
• History feature

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Using Tab Completion
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• 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

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Using the History Feature
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• 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

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The Shell Start-up Process
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• 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

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A Typical Start-up Script
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Customizing the Shell
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• You can customize the Linux environment with the
  following methods
• Use aliases
• Use symbolic links
• Use environment variables

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Using Aliases
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• 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
• aliasltstring enteredgtltstring substituted by the
  shellgt

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Symbolic Links
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• 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

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A Symbolic Link
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Viewing a Symbolic Link
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Environment Variables
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• 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

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Using Text Editors
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• 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

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The Variety of Linux Text Editors
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• 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

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The pico Text Editor
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Using the vi Editor
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• 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

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Using the vi Editor
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vi Commands to Enter Insert or Replace Mode
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Additional vi Commands
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Text Processing
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• There are two methods to create formatted
  documents
• Graphical, or WYSIWYG (what-you-see-is-what-you-ge
  t)
• Rely on markup languages to define special codes
  that format documents

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Markup Languages
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• 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

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An HTML Document in vi
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Controlling Fonts
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• 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

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The xfontsel Program
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The Font Selector Dialog Box in Gnome
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Manipulating Text Files
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• 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

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Linux Text-filtering Commands
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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

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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