2-filehierarchy

Exploring Linux FilesystemsExploring Linux Filesystems

Objectives Understand and navigate the Linux

directory structure using relative andabsolute pathnames

Describe the various types of Linux files View filenames and file types Use shell wildcards to specify multiple

filenames

Understand and navigate the Linuxdirectory structure using relative andabsolute 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

Display the contents of text files andbinary files

Search text files for regular expressionsusing 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 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

Directory: Used to organize other filesinto 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


The Linux Directory Structure(continued)


Figure 3-1: The Windows file system structure

The Linux Directory Structure(continued)

Linux+ Guide to Linux Certification, 3e 6Figure 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 directorytree

cd (change directory) command: changethe current directory in the directory tree Argument specifies the destination directory

Relative pathname: pathname of file ordirectory relative to current directory

Home directory: unique to each user ~ metacharacter used to refer to home directory

pwd (print working directory) command:displays current directory in the directorytree

cd (change directory) command: changethe current directory in the directory tree Argument specifies the destination directory

Relative pathname: pathname of file ordirectory relative to current directory


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

to the root of the tree Referred to by .. (two dots)

Subdirectory: directory residing withinanother directory

Tab-completion: pressing the Tab key fillsin remaining characters of a uniquefilename or directory name BASH shell feature Alerts user if there is more than one possible

match

Parent directory: directory one step closerto the root of the tree Referred to by .. (two dots)

Subdirectory: directory residing withinanother directory

Tab-completion: pressing the Tab key fillsin remaining characters of a uniquefilename or directory name BASH shell feature Alerts user if there is more than one possible

match


Viewing Files and Directories: FileTypes Text files: store information in a readable

text format, contain configurationinformation

Binary data files: store informationassociated with executable programs

Executable program files Directory files: serve as placeholders to

organize other files

Text files: store information in a readabletext format, contain configurationinformation

Binary data files: store informationassociated with executable programs

Executable program files Directory files: serve as placeholders to

organize other files


Viewing Files and Directories: FileTypes (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

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 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

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



Table 3-1: Common filename extensions

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

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


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

Long listing for each file includes eightcomponents File type character List of permissions (mode of the file) Hard link count Owner Group owner File size Most recent modification time Filename


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 touser Configuration files often hidden Filenames start with a dot (.) ls a command: displays hidden files

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 touser Configuration files often hidden Filenames 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 filenames Can match the entire filename or portions of

filenames Can be used with most Linux filesystem

commands

Wildcard metacharacter: used to simplifycommands specifying multiple filenames Can match the entire filename or portions of

filenames Can 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 systemevents New events appended to end

tac command: displays contents of atext file in reverse order

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 systemevents New events appended to end

tac command: displays contents of atext 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 lines Can provide numeric option to specify the

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

head command: view first ten lines of afile

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)


Displaying Content of Text Files(continued) Large text files can not be viewed using

the cat command, because the screenwill 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 morecommand, but can also use cursor toscroll

Large text files can not be viewed usingthe cat command, because the screenwill 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 morecommand, but can also use cursor toscroll


Displaying Content of Text Files(continued) Users can use keyboard shortcuts to

interact with shell while in more and lesscommands. 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 lesscommand

e.g., ls -l | more

Users can use keyboard shortcuts tointeract with shell while in more and lesscommands. 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 lesscommand

e.g., ls -l | more


Displaying the Contents of BinaryFiles 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 inoctal format (numeric base 8 format) -x option displays contents of the file in

hexadecimal format (numeric base 16format)

Typically use program that created thefile

strings command: searches for anddisplays text characters in a binary file Might indicate purpose of binary file

od command: displays contents of file inoctal format (numeric base 8 format) -x option displays contents of the file in

hexadecimal format (numeric base 16format)


Searching for Text Within Files Text tools: commands that search for and

manipulate text Regular expressions (regexp): text

wildcards that ease the search for specifictext Match patterns of text within a text document Used by many text tools and programming

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

more

Text tools: commands that search for andmanipulate text

Regular expressions (regexp): textwildcards that ease the search for specifictext Match patterns of text within a text document Used 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 infilenames; regexps match characters within textfiles

Wildcard metacharacters have differentdefinitions that regexps

More regexps than wildcard metacharacters Regular expressions are divided into

common regexps and extended regexps

Different from wildcard metacharacters Wildcard metacharacters interpreted by shell;

regexps interpreted by text tools Wildcard metacharacters match characters in

filenames; regexps match characters within textfiles

Wildcard metacharacters have differentdefinitions 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 filethat match common regexps

egrep command: displays lines in a textfile that match extended regexps Can be written as grep -E

fgrep command: does not interpret anyregular expressions Returns results much faster than egrep Can be written as grep -F

grep (global regular expression print)command: displays lines in a text filethat match common regexps

egrep command: displays lines in a textfile that match extended regexps Can be written as grep -E

fgrep command: does not interpret anyregular expressions Returns results much faster than egrep Can 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, ignoringdivision into words To search only for occurrences of a word,

surround it by space characters

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, ignoringdivision into words To 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 notrelated to inserting text

Insert mode: Inserts text, but nothing else User environment is customizable

One of the oldest and most popular text editorsfor 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 keysused 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 combinationscommonly used in command mode



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

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

Emacs (Editor MACroS) editor: comparablefunctionality 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


Other Common Text Editors(continued)


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



Figure 3-3: A graphical Emacs session

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

Nano editor: text editor that uses Ctrl keycombinations 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


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

gedit editor: a graphical text editorfunctional 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




Figure 3-4: The gedit text editor

Summary The Linux filesystem is arranged

hierarchically using a series of directoriesto store files

Location of directories and files can bedescribed using absolute or relativepathnames

Linux filesystem can contain many types offiles 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

The Linux filesystem is arrangedhierarchically using a series of directoriesto store files

Location of directories and files can bedescribed using absolute or relativepathnames

Linux filesystem can contain many types offiles 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


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 byseveral utilities, such as head, tail, cat,tac, more, and less

Wildcard metacharacters are specialkeyboard 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 byseveral 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 Linuxsystems

Regular expression metacharacters can beused 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 Linuxsystems


2-filehierarchy

Documents

directory root

theroot directory

level directory

directory tree argument

hierarchical tree directory

changethe current directory

possiblematch parent

home directory pwd print