Week 3 Exploring Linux Filesystems. Objectives Understand and navigate the Linux directory structure using relative and absolute pathnames Describe

Week 3Exploring Linux Filesystems

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 2

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


The Linux Directory Structure Directory: Used to organize other files

into a logical tree structureStored 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 directoryReferred to using the / characterForms root of a hierarchical tree


The Linux Directory Structure (continued)


Figure 3-1: The Windows file system structure

The Linux Directory Structure (continued)


Figure 3-2: The Linux file system structure

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


Changing Directories (continued) Parent directory: directory one step closer

to the root of the treeReferred 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 nameBASH shell featureAlerts user if there is more than one possible

match


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


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


Filenames Filename: identifier given to a file

Up to 255 charactersCan use alphanumeric characters, dash (-),

underscore (_), and dot (.) Filename extensions: identifiers

following a dot (.) at end of filename Denote file typeMost files on Linux do not have filename

extensions



Table 3-1: Common filename extensions

Listing Files

ls command: List the files in a directoryMay pass an argument indicating the

directory to be listed○ –F option: Argument to indicate file types○ –l option: Argument to list long file listings


Listing Files (continued) Long listing for each file includes eight

componentsFile type characterList of permissions (mode of the file)Hard link countOwnerGroup ownerFile sizeMost recent modification timeFilename


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 analyzeIdentifies between different types of executable

filesIdentifies empty files

Hidden files: files not normally displayed to userConfiguration files often hiddenFilenames start with a dot (.)ls –a command: displays hidden files


Listing Files (continued)


Table 3-2: Common options to the ls command

Listing Files (continued)


Table 3-2 (continued): Common options to the ls command

Wildcard Metacharacters

Wildcard metacharacter: used to simplify commands specifying multiple filenamesCan match the entire filename or portions of

filenamesCan be used with most Linux filesystem

commands


Wildcard Metacharacters (continued)


Table 3-3: Wildcard metacharacters

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 eventsNew events appended to end

tac command: displays contents of a text file in reverse order


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 linesCan provide numeric option to specify the

number of lines to be displayed (e.g., head -2 filename)


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-pagePressing Spacebar displays the next pagePressing Enter displays the next line

less command: same as more command, but can also use cursor to scroll


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 screene.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


Displaying the Contents of Binary Files Typically use program that created the

file strings command: searches for and

displays text characters in a binary fileMight 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)


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 textMatch patterns of text within a text documentUsed by many text tools and programming

languages○ Including grep, emacs, C++, PERL, and many

more


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



Table 3-4: Regular expressions

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 regexpsCan be written as grep -E

fgrep command: does not interpret any regular expressions Returns results much faster than egrepCan be written as grep -F


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 wordsTo search only for occurrences of a word,

surround it by space characters


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


Editing Text Files: The vi Editor (continued)


Table 3-5: Common keyboard keys used to change to and from insert mode


32Linux+ Guide to Linux Certification, 3e

Table 3-6: Key combinations commonly used in command mode



Table 3-6 (continued): Key combinations commonly used in command mode



Table 3-6 (continued): Key combinations commonly used in command mode



Table 3-7: Key combinations commonly used at the command mode : prompt

Other Common Text Editors Emacs (Editor MACroS) editor: comparable

functionality to viCtrl 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 editorMuch easier to use; icons replace key

combinations


Other Common Text Editors (continued)


Table 3-8: Keyboard functions commonly used in the GNU Emacs editor



Figure 3-3: A graphical Emacs session


Nano editor: text editor that uses Ctrl key combinations for performing functionsBased on the pine UNIX editorCtrl key combinations listed at the bottom of the

screen

Very basic and easy-to-useUsed by Linux administrators to modify files

when advanced functionality is not needed


Other Common Text Editors (continued) gedit editor: a graphical text editor

functional in a GUI environmentDoes not have advanced functionality like vi

and EmacsEasiest editor to useFunctionality is analogous to the Windows

Wordpad and Notepad editors




Figure 3-4: The gedit text editor

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 filestext 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


Summary (continued) Wildcard metacharacters are special

keyboard characterscan 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


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


Documents

Week 3 Exploring Linux Filesystems. Objectives Understand and navigate the Linux directory structure using relative and absolute pathnames Describe