Linux Guide to Linux Certification, Second Edition

1
Linux Guide to Linux Certification, Second
Edition

• Chapter 4
• Exploring Linux Filesystems

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Objectives

• Understand and navigate the Linux directory
  structure using relative and absolute pathnames
• Describe the various types of Linux files
• View filenames and file types
• Use shell wildcards to specify multiple filenames

3
Objectives (continued)

• Display the contents of text files and binary
  files
• Search text files for regular expressions using
  grep
• Identify common text editors used today
• Use the vi editor to manipulate text files

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The Linux Directory Structure

• Directory Used to organize other files into a
  logical tree structure
• Absolute pathname Pathname from the root
  directory to a certain file or directory
• Root The top level directory
• referred to using the / character

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The Linux Directory Structure (continued)
Figure 4-1 The Windows filesystem structure
Figure 4-2 The Linux filesystem structure
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Changing Directories

• Home directory Unique to each user
• pwd (print working directory) command Displays
  current directory in the directory tree
• cd (change directory) command Change the current
  directory in the directory tree
• metacharacter Refers to home directory
• Relative pathname Pathname of file or directory
  relative to current directory

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Changing Directories (continued)

• Subdirectory Directory residing within another
  directory
• Tab-completion Pressing the Tab key fills in
  remaining characters of a unique filename or
  directory name
• BASH shell feature

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Viewing Files and Directories File Types

• Text files Store information in a readable text
  format
• Binary data files Store information associated
  with executable programs
• Executable program files
• Directory files

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Viewing Files and Directories File Types
(continued)

• Linked files Associated with another file
• Special device files Represent system devices
• Named pipes Identify channel that passes
  information between processes
• Socket files Allow a process on another computer
  to write to a local file

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Filenames

• Filename Identifier given to a file
• Filename extensions Identifiers following a dot
  (.) at end of filename
• Denote file type
• Most files on Linux do not have file extensions

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Filenames (continued)
Table 4-1 Common filename extensions
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Filenames (continued)
Table 4-1 (continued) Common filename extensions
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Listing Files

• ls command List the files in a directory
• May pass an argument indicating the directory to
  be listed
• F switch Argument to list file types
• l switch Argument to list long file listings
• Alias Shortcut for a command
• ll command Alias for ls -l
• File command Displays file type of any file

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Listing Files (continued)

• Hidden files Files not normally displayed to
  user
• Filenames start with a dot (.)
• Configuration files often hidden
• ls a command Displays hidden files

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Listing Files (continued)
Table 4-2 Common options to the ls command
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Listing Files (continued)
Table 4-2 (continued) Common options to the ls
command
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Wildcard Metacharacters

• Wildcard metacharacter Used to simplify commands
  specifying multiple filenames
• Can be used with most Linux filesystem commands

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Wildcard Metacharacters (continued)
Table 4-3 Wildcard metacharacters
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Displaying Content of Text Files

• Concatenation Joining text together
• cat command Displays (concatenates) contents of
  a text file to the screen
• -n switch Displays line number and contents
• Log files Contain records of past system events
• New events appended to end
• tac command Displays files in reverse order
• head command View first few lines of a file

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Displaying Content of Text Files (continued)

• tail command View last few lines of a file
• Can also specify what line number to start at
• more command Displays text files page-by-page
• Space key goes to next page
• Enter key goes to next line
• less command Same as more command, but can also
  use cursor to scroll

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Displaying Content of Text Files (continued)

• more and less can be used with output of other
  commands
• If output is too large to fit on terminal screen,
  use metacharacter
• e.g., ls -l more

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Displaying the Contents of Binary Files

• Typically use program that created the file
• strings command Searches for and displays text
  characters in a binary file
• Might indicate purpose of binary file
• od command Displays contents of file in octal
  format (numeric base 8 format)

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Searching for Text Within Files

• Text tools Search for and manipulate text
• Regular expressions (regexp) Text wildcards that
  assist search for specific text
• Match patterns of text
• Used by many text tools and programming languages
• Including grep, emacs, C, PERL, and many more

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Regular Expressions

• Different from wildcard metacharacters
• Wildcard metacharacters interpreted by shell
  regexps interpreted by text tools
• Wildcard metacharacters match characters in
  filenames regexps match characters within text
  files
• More regexps than wildcard metacharacters
• Common and extended regexps

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Regular Expressions (continued)
Table 4-4 Regular expressions
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Regular Expressions (continued)
Table 4-4 (continued) Regular expressions
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The grep Command

• grep (global regular expression print) command
  Displays lines in a text file matching a given
  regexp
• egrep command Displays lines of text that match
  extended regexps
• fgrep command Does not interpret any regular
  expressions
• Returns results much faster than egrep
• grep requires two arguments
• Text to search for and files to search

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Editing Text Files The vi Editor

• One of the oldest and most popular text editors
  for UNIX OSs
• Vim Linux equivalent of vi
• Standard on most Linux distributions
• Advantage is portability, not usability
• Used on Unix and Linux
• Bi-modal editor (two possible modes)
• Command mode Performs text editing tasks not
  related to inserting text
• Insert mode Inserts text, but nothing else
• User environment is customizable

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Editing Text Files The vi Editor (continued)
Table 4-5 Common keyboard keys used to change to
and from insert mode
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Editing Text Files The vi Editor (continued)
Table 4-6 Key combinations commonly used in
command mode
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Editing Text Files The vi Editor (continued)
Table 4-6 (continued) Key combinations commonly
used in command mode
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Editing Text Files The vi Editor (continued)
Table 4-6 (continued) Key combinations commonly
used in command mode
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Editing Text Files The vi Editor (continued)
Table 4-7 Key combinations commonly used at the
command mode prompt
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Other Common Text Editors

• Mcedit editor (Midnight Commander Editor)
  Easy-to-use text editor
• Supports regexp
• Supports use of mouse for highlighting text
• Emacs (Editor MACroS) editor Comparable
  functionality to vi
• Ctrl key combinations to perform special
  functions
• Supports LISP (LISt Processing) artificial
  intelligence programming language

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Other Common Text Editors (continued)
Table 4-8 Keyboard functions commonly used in
the GNU emacs editor
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Other Common Text Editors (continued)

• Emacs editor is not easy to use
• Must memorize key combinations
• Xemacs editor Version of Emacs for KDE or GNOME
  GUI environments
• Easier to use than emacs
• Not available with every distribution

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Other Common Text Editors (continued)
Figure 4-3 The xemacs text editor
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Other Common Text Editors (continued)

• Graphical text editors available with most Linux
  distributions
• nedit editor
• gedit editor Distributed with GNOME environment
• kedit editor Distributed with KDE environment
• gedit and kedit offer more functionality than
  nedit

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Other Common Text Editors (continued)
Figure 4-4 The nedit text editor
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Other Common Text Editors (continued)
Figure 4-5 The gedit text editor
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Other Common Text Editors (continued)
Figure 4-6 The kedit text editor
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Summary

• The Linux filesystem is arranged hierarchically
  using a series of directories to store files
• Location of these directories and files can be
  described using absolute or relative pathnames
• Accommodates many types of files text files,
  binary data, executable programs, directories,
  linked files, and special device files
• The ls command is used to view filenames
• Wide range of options
• Wildcard metacharacters can simplify selection of
  several files when using common Linux file
  commands

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Summary (continued)

• Text files are the most common file type whose
  contents can be viewed by several utilities, such
  as head, tail, cat, tac, more, and less
• Regular expression metacharacters can be used to
  specify certain patterns of text when used with
  certain programming languages and text tool
  utilities such as grep
• vi (vim) is a powerful, bimodal text editor that
  is standard on most UNIX and Linux systems