1. Linux+ Guide to Linux Certification, Third Edition
Chapter 3
Exploring Linux Filesystems

2. 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
Linux+ Guide to Linux Certification, 3e

3. Objectives (continued)
Display the contents of text files and binary files
Search text files for regular expressions using grep
Use the vi editor to manipulate text files
Identify common alternatives to the vi text editor used today
Linux+ Guide to Linux Certification, 3e

4. The Linux Directory Structure
Directory: Used to organize other files into a logical tree structure
Stored in a filesystem of a specific partition in the hard disk
Absolute pathname: Pathname from the root directory to a certain file or directory
Root: The top level directory
Referred to using the / character
Forms root of a hierarchical tree
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5. The Linux Directory Structure (continued)
Figure 3-1: The Windows filesystem structure
Figure 3-2: The Linux filesystem structure
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6. Changing Directories Home directory: unique to each user
~ metacharacter used to refer to home directory
pwd (print working directory) command: displays current directory in the directory tree
cd (change directory) command: change the current directory in the directory tree
Argument specifies the destination directory
Relative pathname: pathname of file or directory relative to current directory
Linux+ Guide to Linux Certification, 3e

7. Changing Directories (continued)
Parent directory: directory one step closer to the root of the tree
Referred to by .. (two dots)
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
Alerts user if there is more than one possible match
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8. Viewing Files and Directories: File Types
Text files: store information in a readable text format, contain configuration information
Binary data files: store information associated with executable programs
Executable program files
Directory files: serve as placeholders to organize other files
Linux+ Guide to Linux Certification, 3e

9. 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
Linux+ Guide to Linux Certification, 3e

10. Filenames Filename: identifier given to a file
Up to 255 characters
Can use alphanumeric characters, dash (-), underscore (_), and dot (.)
Filename extensions: identifiers following a dot (.) at end of filename
Denote file type
Most files on Linux do not have filename extensions
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11. Table 3-1: Common filename extensions
Linux+ Guide to Linux Certification, 3e

12. Listing Files ls command: List the files in a directory
May pass an argument indicating the directory to be listed
–F option: Argument to indicate file types
–l option: Argument to list long file listings
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13. Listing Files (continued)
Long listing for each file includes eight components
File type character
List of permissions (mode of the file)
Hard link count
Owner
Group owner
File size
Most recent modification time
Filename
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14. Listing Files (continued)
Alias: shortcut for a command
ll command: Alias for ls -l
File command: displays file type of any file
Argument indicates what file or files to analyze
Identifies between different types of executable files
Identifies empty files
Hidden files: files not normally displayed to user
Configuration files often hidden
Filenames start with a dot (.)
ls –a command: displays hidden files
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15. Listing Files (continued)
Table 3-2: Common options to the ls command
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16. Listing Files (continued)
Table 3-2 (continued): Common options to the ls command
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17. Wildcard Metacharacters
Wildcard metacharacter: used to simplify commands specifying multiple filenames
Can match the entire filename or portions of filenames
Can be used with most Linux filesystem commands
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18. Wildcard Metacharacters (continued)
Table 3-3: Wildcard metacharacters
Linux+ Guide to Linux Certification, 3e

19. Displaying Content of Text Files
Concatenation: joining text together
cat command: displays (concatenates) contents of a text file to the screen
-n option: displays line number and contents
Log files: contain records of past system events
New events appended to end
tac command: displays contents of a text file in reverse order
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20. Displaying Content of Text Files (Continued)
head command: view first ten lines of a file
tail command: view last ten lines of a file
For head and tail commands
Line count includes blank lines
Can provide numeric option to specify the number of lines to be displayed (e.g., head -2 filename)
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21. Displaying Content of Text Files (continued)
Large text files can not be viewed using the cat command, because the screen will only fit a portion of the file
more command: displays text files page-by-page
Pressing Spacebar displays the next page
Pressing Enter displays the next line
less command: same as more command, but can also use cursor to scroll
Linux+ Guide to Linux Certification, 3e

22. Displaying Content of Text Files (continued)
Users can use keyboard shortcuts to interact with shell while in more and less commands.
e.g., pressing h key gets Help screen
e.g., pressing q key quits more and less commands
more and less can be used with output of other commands
If output is too large to fit on terminal screen, use “|” metacharacter and more or less command
e.g., ls -l | more
Linux+ Guide to Linux Certification, 3e

23. 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)
-x option displays contents of the file in hexadecimal format (numeric base 16 format)
Linux+ Guide to Linux Certification, 3e

24. Searching for Text Within Files
Text tools: commands that search for and manipulate text
Regular expressions (regexp): text wildcards that ease the search for specific text
Match patterns of text within a text document
Used by many text tools and programming languages
Including grep, emacs, C++, PERL, and many more
Linux+ Guide to Linux Certification, 3e

25. 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
Wildcard metacharacters have different definitions that regexps
More regexps than wildcard metacharacters
Regular expressions are divided into common regexps and extended regexps
Linux+ Guide to Linux Certification, 3e

26. Table 3-4: Regular expressions
Linux+ Guide to Linux Certification, 3e

27. The grep Command
grep (global regular expression print) command: displays lines in a text file that match common regexps
egrep command: displays lines in a text file that match extended regexps
Can be written as grep -E
fgrep command: does not interpret any regular expressions
Returns results much faster than egrep
Can be written as grep -F
Linux+ Guide to Linux Certification, 3e

28. The grep Command (continued)
grep requires two arguments
Text to search for
Can use regular expressions
Files in which to search
grep is case sensitive
For case-insensitive search, use –i option
grep matches patterns of text, ignoring division into words
To search only for occurrences of a word, surround it by space characters
Linux+ Guide to Linux Certification, 3e

29. 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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30. Editing Text Files: The vi Editor (continued)
Table 3-5: Common keyboard keys used to change to and from insert mode
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31. Editing Text Files: The vi Editor (continued)
Table 3-6: Key combinations commonly used in command mode
Linux+ Guide to Linux Certification, 3e

32. Editing Text Files: The vi Editor (continued)
Table 3-6 (continued): Key combinations commonly used in command mode
Linux+ Guide to Linux Certification, 3e

33. Editing Text Files: The vi Editor (continued)
Table 3-6 (continued): Key combinations commonly used in command mode
Linux+ Guide to Linux Certification, 3e

34. Editing Text Files: The vi Editor (continued)
Table 3-7: Key combinations commonly used at the command mode : prompt
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35. Other Common Text Editors
Emacs (Editor MACroS) editor: comparable functionality to vi
Ctrl key combinations to perform special functions
Supports LISP (LISt Processing) artificial intelligence programming language
Emacs editor is not easy to use
Must memorize key combination
Emacs can be run in a GUI environment to get a graphical version of the editor
Much easier to use; icons replace key combinations
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36. Other Common Text Editors (continued)
Table 3-8: Keyboard functions commonly used in the GNU Emacs editor
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37. Other Common Text Editors (continued)
Figure 3-3: A graphical Emacs session
Linux+ Guide to Linux Certification, 3e

38. Other Common Text Editors (continued)
Nano editor: text editor that uses Ctrl key combinations for performing functions
Based on the pine UNIX editor
Ctrl key combinations listed at the bottom of the screen
Very basic and easy-to-use
Used by Linux administrators to modify files when advanced functionality is not needed
Linux+ Guide to Linux Certification, 3e

39. Other Common Text Editors (continued)
gedit editor: a graphical text editor functional in a GUI environment
Does not have advanced functionality like vi and Emacs
Easiest editor to use
Functionality is analogous to the Windows Wordpad and Notepad editors
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40. Other Common Text Editors (continued)
Figure 3-4: The gedit text editor
Linux+ Guide to Linux Certification, 3e

41. Summary
The Linux filesystem is arranged hierarchically using a series of directories to store files
Location of directories and files can be described using absolute or relative pathnames
Linux filesystem can contain 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 to modify views
Linux+ Guide to Linux Certification, 3e

42. Summary (continued)
Wildcard metacharacters are special keyboard characters
can simplify selection of several files when using common Linux file commands
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
Linux+ Guide to Linux Certification, 3e

43. Summary (continued)
Regular expression metacharacters can be used to specify certain patterns of text
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
Linux+ Guide to Linux Certification, 3e