SUSE Linux Enterprise Desktop Administration

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SUSE Linux Enterprise Desktop Administration

• Chapter 8
• Work with the Linux Shell and Command Line

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Objectives

• Objective 1Get to Know the bash Shell
• Objective 2Get to Know Common Command-Line Tasks
• Objective 3Understand Command Syntax and Special
  Characters
• Objective 4Get to Know Linux Text Editors

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Objective 1Get to Know the bash Shell

• Shell
• Accepts a users entries, interprets them,
  converts them to system calls, and delivers
  system messages back to the user, making it a
  command interpreter
• To understand the bash shell, you need to know
  the following
• Types of Shells
• bash Configuration Files
• Completion of Commands and Filenames
• History Function

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Types of Shells

• Examples of some popular shells
• The Bourne Shell (/bin/sh symbolic link to
  /bin/bash)
• The Bourne Again Shell (/bin/bash)
• The Korn shell (/bin/ksh)
• The C shell (/bin/csh symbolic link to
  /bin/tcsh)
• The TC shell (/bin/tcsh)
• Shells differ in the functionality they provide
• Every shell can be started like a program
• You can switch at any time to a different shell

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Types of Shells (continued)

• The shell does not terminate on its own
• You need to enter the exit command to return to
  the previous shell
• Login shell
• A shell is started at a text console right after
  a user logs in
• Which shell is started for which user is defined
  in the user database
• The standard Linux shell is bash

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bash Configuration Files

• Login shells
• Started whenever a user logs in to the system or
  a user logs in through an X display manager
• The following files are read when starting a
  login shell
• /etc/profile
• /etc/bash.bashrc
• For your own systemwide bash configurations, use
  the file /etc/bash.bashrc.local
• /.bashrc
• Configuration file in which users store their
  customizations

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bash Configuration Files (continued)

• Nonlogin shells
• The following files are read when starting a
  nonlogin shell
• /etc/bash.bashrc
• /etc/bash.bashrc.local
• /.bashrc
• SLED has a default setup that ensures users do
  not see any difference between both types of
  shell
• To read in a changed configuration file and to
  apply the changes to the current session
• Use the internal shell source command

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Completion of Commands and Filenames

• The bash shell supports a function of completing
  commands and filenames
• Just enter the first characters of a command (or
  a filename) and press Tab
• If more than one possibility exists
• The bash shell shows all possibilities when you
  press Tab a second time

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History Function

• bash stores the commands you enter so you have
  easy access to them again when needed later
• By default, the commands are written in the
  .bash_history file in the users home directory
• You can display the content of the file by using
  the history command
• You can display the commands stored in the
  history cache (one at a time) by using the arrow
  keys
• Enter part of the command and press Ctrlr
• To search the history list for matching commands
  and display them

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Objective 2Get to Know Common Command-Line Tasks

• Two features make working with the bash shell
  more powerful
• Variables
• Aliases

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Variables

• Environment variables
• Control the behavior of a program that is started
  from a shell
• Shell variables
• Control the behavior of the shell itself
• Some important environment variables include the
  following
• PATH
• HOME
• USER

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Variables (continued)

• To display the value of a shell or environment
  variable, enter echo variable
• To set the value of a variable or to create a new
  variable, use the syntax variablevalue

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Aliases

• Allow you to create shortcuts for commands and
  their options
• Or to create commands with entirely different
  names
• You can find out about the aliases defined on
  your system with the alias command
• To see whether a given command is an alias for
  something else, use the type command

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Aliases (continued)

• Most of the aliases used on a systemwide basis
  are defined in the file /etc/bash.bashrc
• Aliases are defined with the alias command and
  can be removed with the unalias command
• Syntax for defining aliases
• alias aliasnamecommand options
• An alias defined in this way is only valid for
  the current shell
• To make an alias persistent, you need to store
  the definition in one of the shells
  configuration files

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Exercise 8-1 Execute Commands at the Command Line

• In this exercise, use the history feature of the
  shell
• Then create an alias labeled hello that prints a
  personal welcome message, Hello username, on the
  screen
• Finally, remove this alias

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Objective 3Understand Command Syntax and Special
Characters

• You can use specific characters to provide
  special functionality
• In this objective, you learn about the following
• Select Your Character Encoding
• Name Expansion Using Search Patterns
• Prevent the Shell from Interpreting Special
  Characters

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Select Your Character Encoding

• Variables are used to determine the localization
• Use the locale command to get a list of the
  localization variables

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Select Your Character Encoding (continued)

• The variable LANG specifies the language
• SUSE Linux Enterprise Desktop uses UTF-8 encoding
  for all users, except the user root
• The output of some commands depends on the type
  of encoding

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Name Expansion Using Search Patterns

• Occasionally, you might want to perform
  operations on a series of files without having to
  name all the files
• In this case, you could make use of the search
  patterns shown in Table 8-1
• If search patterns (wildcards) are given on the
  command line
• The shell tries to compare these with the
  filenames in the file system and, if they match,
  the expression is replaced with all the filenames
  found

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Name Expansion Using Search Patterns (continued)
Table 8-1 Search patterns
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Prevent the Shell from Interpreting Special
Characters

• To prevent the shell from interpreting special
  characters in the command line
• They must be masked by using the following
• \

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Exercise 8-2 Work with Command Syntax and
Special Characters

• In this exercise, you learn how to use wildcards
  and other special characters
• Change the character encoding from UTF-8 to POSIX
  
• Then, list all filenames in the /bin directory
  that
• Start with the character a
• Consist of four characters
• Consist of four or more characters
• Do not start with any of the characters from a to
  r

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Exercise 8-2 Work with Command Syntax and
Special Characters (continued)

• In the next part of this exercise, use the
  Nautilus file manager to create new files named
  My, File, and My File
• Then, list the files and remove them
• To do this, you have to mask special characters

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Objective 4Get to Know Linux Text Editors

• Several text editors are available in Linux,
  including
• vi
• emacs
• xemacs
• xedit
• gedit
• kwrite
• Two types of editors exist
• Graphical editors
• Command-line editors

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Work with gedit (Graphical Editor)

• The gedit editor can be started from the main
  menu (Computer gt More Applications gt Tools gt
  gedit)
• See Figure 8-1

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Figure 8-1 The gedit editor
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Work with vi (Command-Line Editor)

• The advantage of command-line editors
• You can use them without having a graphical
  desktop environment installed
• vi is used by most administrators because it is
  available on every Linux and UNIX system
• Always available, even on the rescue system
• In SUSE Linux Enterprise Desktop, vim (vi
  improved) by Bram Moolenaar is the standard vi
  editor

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Start vi

• You can start vi by entering vi or vim in a
  terminal window
• See Figure 8-2

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Figure 8-1 The vi editor
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Use the Editor vi

• You can move the cursor
• With the k, j, h, and l keys (kone line up,
  jone line down, hto the left, lto the right)
• By using the arrow keys (Up-arrow, Down-arrow,
  Left-arrow, Right-arrow)

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Learn the Working Modes

• vi is mode-oriented
• When vi is first started, it is in command mode
• Anything you enter is considered a command
• To enter text, you must first switch the editor
  to insert mode by
• Typing i (insert)
• Pressing the Insert key
• Press Esc once to take you back to command mode
• From command mode, you can switch to command-line
  mode by entering

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Learn the Working Modes (continued)

• Available modes
• Command mode
• Insert mode
• Command-line mode

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Learn the Working Modes (continued)
Table 8-2 Commands in the vi command mode
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Learn the Working Modes (continued)
Table 8-3 Commands in the vi command-line mode
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Exercise 8-3 Use vi to Edit Files in the Linux
System

• In this exercise, create a new vi_test file with
  the text editor vi
• Then, edit the text in the command mode of vi

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Summary

• After logging in to a Linux system, a login shell
  is started
• Although there are many shells available for use
  in Linux, the default shell is the Bourne Again
  Shell (bash)
• The bash shell is case-sensitive
• Several environment variables are loaded when a
  shell is started that is used by programs to set
  the user environment and locale
• Aliases are special shell variables that contain
  commands

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Summary (continued)

• Wildcards are special characters that can be used
  to represent patterns when specifying file or
  directory names on the file system
• Although many text-based and graphical text
  editors are available for Linux systems, the vi
  editor is the most commonly used editor across
  different distributions of Linux and versions of
  UNIX