part one the essence of unix. 2 overview unix history –origins, versions, distributions using unix...

Part OnePart One

The Essence of UNIXThe Essence of UNIX

22

OverviewOverview

Unix historyUnix history– Origins, versions, distributionsOrigins, versions, distributions

Using UnixUsing Unix– Log in/outLog in/out

Unix shellsUnix shells

Basic commandsBasic commands

Editor(s)Editor(s)

Compile a C/C++ programCompile a C/C++ program

33

Introducing the UNIXIntroducing the UNIXOperating SystemOperating System

UNIX is a multi-user systemUNIX is a multi-user system– Allows many users access and share the Allows many users access and share the

resources of a server computerresources of a server computer

UNIX is a multitasking systemUNIX is a multitasking system– Allows user to execute more than one Allows user to execute more than one

program at a timeprogram at a time

UNIX is a portable operating systemUNIX is a portable operating system– Used in many computing environmentsUsed in many computing environments

44

Unix HistoryUnix History

Bell Labs …Bell Labs …

UC Berkeley …UC Berkeley …

Commercial versions:Commercial versions:– Solaris, Irix, HP/UX, Ultrix, SCO Unix, AIX, …Solaris, Irix, HP/UX, Ultrix, SCO Unix, AIX, …

Open source versions:Open source versions:– FreeBSDFreeBSD– LinuxLinux

55

Linux and UNIXLinux and UNIX

Linux is UNIX-likeLinux is UNIX-like– Created by Linus TorvaldsCreated by Linus Torvalds– Not written from traditional UNIX codeNot written from traditional UNIX code

Linux is original codeLinux is original code– follows POSIX standardsfollows POSIX standards

66

Linux StructureLinux Structure

77

Linux DistributionsLinux Distributions

Many companies have createdMany companies have created Linux distributionsLinux distributions

distributions contain distributions contain – source code for the Linux kernel and utilitiessource code for the Linux kernel and utilities– installation toolsinstallation tools– professional documentationprofessional documentation– technical support,technical support,– specialized softwarespecialized software

They can charge as much as they choose for their They can charge as much as they choose for their Linux distributionsLinux distributions

88

Linux DistributionsLinux Distributions

99

UNIX ConceptsUNIX Concepts

ShellShell– The interface between user and OSThe interface between user and OS

Hierarchical StructureHierarchical Structure– Directory and subdirectory organizationDirectory and subdirectory organization

Layered componentsLayered components– Layers of software cover hardwareLayers of software cover hardware

1111

Choosing Your ShellChoosing Your Shell

Shells interpret commands and act as first-class Shells interpret commands and act as first-class programming languageprogramming language

A default shell is associated with your account A default shell is associated with your account when createdwhen created

A list of some UNIX shells:A list of some UNIX shells:– BourneBourne– C shellC shell– KornKorn– Bash, tcshBash, tcsh

1212

Choosing User Names Choosing User Names and Passwordsand Passwords

To use UNIX, a user must log in by providing a To use UNIX, a user must log in by providing a unique user name and passwordunique user name and password

UNIX system administrators create accounts by UNIX system administrators create accounts by adding user names and passwordsadding user names and passwords

1313

Connecting to a UNIX SystemConnecting to a UNIX System

Directly via attached terminalDirectly via attached terminal

Via terminal window in windowing systemVia terminal window in windowing system

Remotely through telnet, rsh or sshRemotely through telnet, rsh or ssh

1414

Connecting to UNIXConnecting to UNIXUsing TelnetUsing Telnet

telnet is terminal emulation softwaretelnet is terminal emulation software– Deemed insecureDeemed insecure– Better: sshBetter: ssh

connects to Unix serverconnects to Unix server– Once connected to a UNIX host, work with Once connected to a UNIX host, work with

UNIX may beginUNIX may begin– Uses IP addresses or domain names to Uses IP addresses or domain names to

access remote systemsaccess remote systems

1515

Entering CommandsEntering Commands

To interact with UNIX, a command is entered To interact with UNIX, a command is entered at the command promptat the command prompt

UNIX is case-sensitive and most commands UNIX is case-sensitive and most commands are typed in lower caseare typed in lower case

Two categories of commandsTwo categories of commands– User-level: perform tasksUser-level: perform tasks– System administration: system managementSystem administration: system management

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The date commandThe date command– Displays the system date, which the system Displays the system date, which the system

administrator maintainsadministrator maintains

The cal commandThe cal command– Shows the system calendarShows the system calendar

The who commandThe who command– Shows who is using the system and their Shows who is using the system and their

current locationcurrent location

1717


1818


1919


2020


Command-line editing (shell dependent)Command-line editing (shell dependent)– Certain keystrokes perform command-line Certain keystrokes perform command-line

editingediting– Use up and down arrow keys to scroll Use up and down arrow keys to scroll

through command historythrough command history

Multiple command entryMultiple command entry– Separate commands with semicolon(;)Separate commands with semicolon(;)The clear commandThe clear command– Clears the current screenClears the current screen

2121

Getting HelpGetting Help

The man program displays the UNIX online reference The man program displays the UNIX online reference manual, called the man pages, for help purposesmanual, called the man pages, for help purposes

2222

Viewing FilesViewing Files

Use cat, more, and less to view an entire Use cat, more, and less to view an entire file contentsfile contents– cat displays a whole file at one timecat displays a whole file at one time– more displays a file one screen at a time, more displays a file one screen at a time,

allowing scroll down allowing scroll down

– less displays a file one screen at a time, less displays a file one screen at a time, allowing scroll down and upallowing scroll down and up

2323

Viewing FilesViewing Files

Use head and tail to view the first few or Use head and tail to view the first few or last few lines of a filelast few lines of a file– head displays the first few lineshead displays the first few lines– tail displays the last few linestail displays the last few lines

2424

Logging Out of UNIXLogging Out of UNIX

Logging out ends your current process Logging out ends your current process and indicates to UNIX that you are and indicates to UNIX that you are finishedfinished

Logging out is shell dependentLogging out is shell dependent– Bourne, Korn, Bash – exit commandBourne, Korn, Bash – exit command– C shell – logout commandC shell – logout command

2525

Changing PasswordsChanging Passwords

For security purposes, changing For security purposes, changing passwords is necessarypasswords is necessary– Use the passwd commandUse the passwd command– UNIX allows new password if:UNIX allows new password if:

The new password differs by at least three The new password differs by at least three characterscharactersIt has six or more characters, including at least It has six or more characters, including at least two letters and one numbertwo letters and one numberIt is different from the user nameIt is different from the user name

2626

Understanding the Role of the Understanding the Role of the UNIX System AdministratorUNIX System Administrator

User “root” manages the UNIX systemUser “root” manages the UNIX system– Adds users and deletes old accountsAdds users and deletes old accounts– Also called the superuserAlso called the superuser– Unlimited permission to alter systemUnlimited permission to alter system

Unix file systemUnix file system

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Understanding the UNIXUnderstanding the UNIXFile SystemFile System

A file is the basic component for data storageA file is the basic component for data storage– UNIX considers everything it interacts with a fileUNIX considers everything it interacts with a file

A file system is UNIX’s way of organizing files on A file system is UNIX’s way of organizing files on mass storage (disk) devicesmass storage (disk) devices– A physical file system is a section of the hard disk that A physical file system is a section of the hard disk that

has been formatted to hold fileshas been formatted to hold files

The file system is organized in a hierarchical The file system is organized in a hierarchical structure similar to an inverted treestructure similar to an inverted tree

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Understanding the Standard Understanding the Standard Tree StructureTree Structure

The structure starts at the root levelThe structure starts at the root level– Root is the name of the file at this basic level and it is Root is the name of the file at this basic level and it is

denoted by the slash character (/)denoted by the slash character (/)

A directory is a file that can contain other files A directory is a file that can contain other files and directoriesand directories

A subdirectory is a directory within a directoryA subdirectory is a directory within a directory– The subdirectory is considered the child of the parent The subdirectory is considered the child of the parent

directorydirectory

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Exploring the Root File System Exploring the Root File System

UNIX must mount a file system before any UNIX must mount a file system before any programs can access files on itprograms can access files on it

To mount a file system is to connect it to To mount a file system is to connect it to the directory tree structurethe directory tree structure

The root file system is mounted by the The root file system is mounted by the kernel when the system startskernel when the system starts

3232

Exploring the Root File Exploring the Root File System System

The root directory contains sub-directories The root directory contains sub-directories that contain files:that contain files:– /bin/bin contains binaries, or executables needed contains binaries, or executables needed

to start the system and perform system tasksto start the system and perform system tasks– /boot/boot contains files needed by the bootstrap contains files needed by the bootstrap

loader as well as kernel imagesloader as well as kernel images– /dev/dev contains system device reference files contains system device reference files

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Root subdirectories continued:Root subdirectories continued:– /etc/etc contains configuration files that the contains configuration files that the

system uses when the computer startssystem uses when the computer starts– /lib/lib contains kernel modules, security contains kernel modules, security

information, and the shared library imagesinformation, and the shared library images– /mnt/mnt contains mount points for temporary contains mount points for temporary

mounts by the system administratormounts by the system administrator– /proc/proc is a virtual file system allocated in is a virtual file system allocated in

memory onlymemory only

3535


Root subdirectories continued:Root subdirectories continued:– /root/root is the home directory of the root user, or is the home directory of the root user, or

the system administratorthe system administrator– /sbin/sbin contains essential network programs contains essential network programs

used only by the system administrator used only by the system administrator – /tmp/tmp is a temporary place to store data during is a temporary place to store data during

processing cyclesprocessing cycles– /var/var contains subdirectories which have sizes contains subdirectories which have sizes

that often change, such as error logsthat often change, such as error logs

3636

Understanding PathsUnderstanding Pathsand Pathnamesand Pathnames

To specify a file or directory, use its To specify a file or directory, use its pathname, which follows the branches of pathname, which follows the branches of the file system to the desired filethe file system to the desired file– A forward slash (/) separates each directory A forward slash (/) separates each directory

namename– The UNIX command prompt may indicate The UNIX command prompt may indicate

your location within the file systemyour location within the file system– Use the UNIX pwd command to display the Use the UNIX pwd command to display the

current path namecurrent path name

3737

Navigating the File System Navigating the File System

To navigate the UNIX directory structure, To navigate the UNIX directory structure, use the cd (change directory) commanduse the cd (change directory) command

UNIX refers to a path as either:UNIX refers to a path as either:– Absolute - begins at the root level and lists all Absolute - begins at the root level and lists all

subdirectories to the destination filesubdirectories to the destination file– Relative - begins at your current working Relative - begins at your current working

directory and proceeds from there directory and proceeds from there

3838

Listing Directory ContentsListing Directory Contents

The ls (list) command displays a directory’s contents, The ls (list) command displays a directory’s contents,

including files and subdirectoriesincluding files and subdirectories

3939


ls options:ls options:– aa include files with “.”include files with “.”– ll long formatlong format– RR recursively list subdirectoriesrecursively list subdirectories

4040


4141

Managing Directories and Managing Directories and FilesFiles

mkdir (make directory) commandmkdir (make directory) command– Create a new directoryCreate a new directory

rmdir (make directory) commandrmdir (make directory) command– Delete an empty directoryDelete an empty directory

cp (copy) commandcp (copy) command– Copy files from one director to anotherCopy files from one director to another

rm (remove) commandrm (remove) command– Delete filesDelete files

4242

Setting File PermissionsSetting File Permissions

4343

Setting File PermissionsSetting File Permissions

File PermissionsFile Permissions

rr Owner has readOwner has read

ww Owner has writeOwner has write

xx Owner has executeOwner has execute

rr Group has readGroup has read

-- Group does not have writeGroup does not have write

xx Group has executeGroup has execute

rr Others have readOthers have read

-- Others do not have writeOthers do not have write

xx Others have executeOthers have execute

4444

Setting File PermissionsSetting File Permissionsfor Securityfor Security

chmod commandchmod command– To set file permissionsTo set file permissions– Settings are read (r), write (w), execute (x)Settings are read (r), write (w), execute (x)– The three types of users are owners, groups, The three types of users are owners, groups,

and othersand others

Setting permissions to directoriesSetting permissions to directories– Use the execute (x) to grant accessUse the execute (x) to grant access

4545

Using Input and Error Using Input and Error RedirectionRedirection

You can use redirection operators to retrieve You can use redirection operators to retrieve input from something other than the standard input from something other than the standard input device and send output to something other input device and send output to something other than the standard output device than the standard output device

Examples of redirection:Examples of redirection:– Redirect the ls command output to a file, instead of to Redirect the ls command output to a file, instead of to

the monitor (or screen)the monitor (or screen)– Redirect a program that receives input from the Redirect a program that receives input from the

keyboard to receive input from a file insteadkeyboard to receive input from a file instead– Redirect error messages to files, instead of to the Redirect error messages to files, instead of to the

screen by defaultscreen by default

4646

Redirecting OutputRedirecting Output

The greater than sign (>) is called a The greater than sign (>) is called a redirection symbolredirection symbol

Create a new file or overwrite an existing Create a new file or overwrite an existing file by attaching (>) to a command that file by attaching (>) to a command that produces outputproduces output

To append to an existing file, use two To append to an existing file, use two redirection symbols (>>)redirection symbols (>>)

4747

Creating new filesCreating new files

using cat output redirectionusing cat output redirectionconcatenate text via output redirectionconcatenate text via output redirection

touch command on new filetouch command on new fileinvoke editor for new fileinvoke editor for new file

4848

Manipulating FilesManipulating Files

Delete files when you no longer neededDelete files when you no longer needed– rm command rm command

permanently removes a file or an empty directorypermanently removes a file or an empty directory

-r option removes a directory and everything it contains -r option removes a directory and everything it contains

Copy files as a means of back-up or as a means Copy files as a means of back-up or as a means to assist with new file creationto assist with new file creation– cp commandcp command

copies the file(s) specified by the source path to the location copies the file(s) specified by the source path to the location specified by the destination path specified by the destination path

4949


Moving a fileMoving a file– mv commandmv command

removes file from one directory and places it in removes file from one directory and places it in anotheranother

Finding a file helps you locate it in the Finding a file helps you locate it in the directory structuredirectory structure– find commandfind command

searches for the file that has the name you specifysearches for the file that has the name you specify

5050


Combining files using output redirectionCombining files using output redirection– cat commandcat command

concatenate text of two different files via output redirectionconcatenate text of two different files via output redirection

– paste commandpaste commandjoins text of different files in side by side fashionjoins text of different files in side by side fashion

Extracting fields of a file using output redirectionExtracting fields of a file using output redirection– cut commandcut command

removes specific columns or fields from a fileremoves specific columns or fields from a file

5151

Sorting FilesSorting Files

sortsort command command– sort options:sort options:

alphabetical or numerical sortalphabetical or numerical sort

specify sort key(s)specify sort key(s)

5252

Commands as filtersCommands as filters

pipe operator (|) pipe operator (|)

redirects the output of one commandredirects the output of one command

to the input of another command to the input of another command – Example: redirect output of “ls” to “more”Example: redirect output of “ls” to “more”

pipe operator can connect several pipe operator can connect several commands on the same command linecommands on the same command line

5353

Using PipesUsing Pipes

Using pipe operators and connecting commands is useful when viewing directory information

5454

Using the grep CommandUsing the grep Command

searches for a specific pattern in a file, such as searches for a specific pattern in a file, such as a word or phrasea word or phrase

grep’s options and wildcard support allow for grep’s options and wildcard support allow for powerful search operationspowerful search operations

You can increase grep’s usefulness by You can increase grep’s usefulness by combining with other commands, such as head combining with other commands, such as head or tailor tail

5555

Using the grep CommandUsing the grep Command

grep can be part of pipe

5656

Regular expressionsRegular expressions

Character matchingCharacter matching– Each character matches itselfEach character matches itself– . Matches any character. Matches any character– ^ line-begin, $ line-end^ line-begin, $ line-end– [abc] [a-z] [0-9a-zA-Z][abc] [a-z] [0-9a-zA-Z]

matches one of the charactersmatches one of the characters

– [:digit:] [:lower:] [:upper:] [:alnum][:digit:] [:lower:] [:upper:] [:alnum]– [^abc][^abc]

Matches everything elseMatches everything else

Repetition: *Repetition: *

5757

Extended regular expressionsExtended regular expressions

Repetitions:Repetitions:– * zero or more* zero or more– + one or more+ one or more– ? zero or one? zero or one– {n} exactly n times{n} exactly n times– {n,m} at least n, at most m{n,m} at least n, at most m– {n,} at least n times{n,} at least n times

Grouping:Grouping:– ( )( )– | | logical or logical or

5858

grep versionsgrep versions

grepgrep– Supports basic regular expressionsSupports basic regular expressions

egrepegrep– supports extended regular expressionssupports extended regular expressions

fgrepfgrep– searches for fixed stringssearches for fixed strings

5959

Using the diff CommandUsing the diff Command

determines the minimal changes needed determines the minimal changes needed to convert file1 to file2to convert file1 to file2

output displays the line(s) that differoutput displays the line(s) that differ

output contains codes to indicate which output contains codes to indicate which lines must be added, changed or deletedlines must be added, changed or deleted

applied via applied via patchpatch command command

6060

Using the Manipulate and Using the Manipulate and Format CommandsFormat Commands

These commands are: sed, trThese commands are: sed, tr

Used to edit and transform the Used to edit and transform the appearance of data before it is appearance of data before it is displayed or printeddisplayed or printed

Example of trExample of tr– cat file | tr ‘:’ ‘/’ > newfilecat file | tr ‘:’ ‘/’ > newfile

6161

Stream editor: sedStream editor: sed

sed is a UNIX editor that allows you to make sed is a UNIX editor that allows you to make global changes to large filesglobal changes to large files

Minimum requirements are an input file and a Minimum requirements are an input file and a command that lets sed know what actions to command that lets sed know what actions to apply to the fileapply to the file

sed commands have two general formssed commands have two general forms– Specify an editing command on the command lineSpecify an editing command on the command line– Specify a script file containing sed commandsSpecify a script file containing sed commands

6262

sed command examplessed command examples

command language similar to vicommand language similar to vi

syntax: syntax: – address-range commandaddress-range command

examples:examples:– 1,$ s/one/two/1,$ s/one/two/

– 5 p5 p

– 1,29 d1,29 d

6363

vi editorvi editor

6464

Using the vi EditorUsing the vi Editor

Called vi because it is visual – it immediately Called vi because it is visual – it immediately displays on screen the changes that you make displays on screen the changes that you make to textto text

It is also modal – works in three modesIt is also modal – works in three modes– Insert mode - lets you enter textInsert mode - lets you enter text– Command mode - lets you enter commands to Command mode - lets you enter commands to

perform editing tasksperform editing tasks– Extended (ex) command set mode - lets you use an Extended (ex) command set mode - lets you use an

extended set of editing commands extended set of editing commands

6565


To create a new file in the vi editor, type vi and the name of the new file at the command prompt

6666


When started, the vi editor is in command When started, the vi editor is in command modemode– In order to insert text, you must issue the “i” In order to insert text, you must issue the “i”

command to enter insert modecommand to enter insert mode– You can repeat the line just entered with the You can repeat the line just entered with the

repeat command (.)repeat command (.)– To edit what you’ve just typed, move the To edit what you’ve just typed, move the

cursor with the various keyboard cursor cursor with the various keyboard cursor movement keysmovement keys

6767


In insert mode, every character you type appears on the screen

6868


The repeat command repeats the last insertion, or line. Now, edit the new line in order to create the next item

6969


7070


While still in command mode:While still in command mode:– To delete text, move to a character and then To delete text, move to a character and then

type “x”type “x”– You can undo a command (reverse its effects) You can undo a command (reverse its effects)

by typing “u”by typing “u”– To search for a text pattern, type a forward To search for a text pattern, type a forward

slash (/), type the pattern, and press Enterslash (/), type the pattern, and press Enter

7171


7272


7373


The status line at the bottom of the screen displays information, including line-oriented commands and error messages

7474


During text searches, you can replace, too. Use line-oriented commands in ex mode to perform this action

7575


Saving a File and Exiting viSaving a File and Exiting vi– You should always save the file before exiting You should always save the file before exiting

vi, otherwise changes are lostvi, otherwise changes are lost– To save a file and continue working on it, type To save a file and continue working on it, type

the :w (write) commandthe :w (write) command– While in command mode, use the :wq (write While in command mode, use the :wq (write

and quit) command to save and exit, or the ZZ and quit) command to save and exit, or the ZZ command to exit after saving command to exit after saving

7676


In vi, you can also:In vi, you can also:– Add text from another fileAdd text from another file– Leave vi temporarily to perform other UNIX Leave vi temporarily to perform other UNIX

tasks, then return to your filetasks, then return to your file– Change your display while editing, such as Change your display while editing, such as

adding line numbering to help editingadding line numbering to help editing– Copy, cut, and paste text to help editingCopy, cut, and paste text to help editing– Print text filesPrint text files– Cancel an editing sessionCancel an editing session

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7878

UNIX UtilitiesUNIX Utilities

UNIX utilities let you create and manage files, UNIX utilities let you create and manage files, run programs, produce reports, and generally run programs, produce reports, and generally interact with the systeminteract with the system

They also offer a full range of services that let They also offer a full range of services that let you monitor and maintain the system and you monitor and maintain the system and recover from a wide range of errorsrecover from a wide range of errors

Utility programs are vital for working through an Utility programs are vital for working through an OS and new utilities are continually being added OS and new utilities are continually being added in order to make UNIX run more efficientlyin order to make UNIX run more efficiently

7979

UNIX UtilitiesUNIX Utilities

UNIX utilities are classified into seven major UNIX utilities are classified into seven major function areas dictated by user needs function areas dictated by user needs – File processingFile processing– System statusSystem status– NetworkingNetworking– CommunicationsCommunications– ProgrammingProgramming– Source code managementSource code management– MiscellaneousMiscellaneous

8989

C Programming in aC Programming in a

UNIX EnvironmentUNIX Environment

9191

Creating a C ProgramCreating a C Program#include <stdio.h>

main() { printf("hello world\n");}

Stored as:Stored as: one.cone.c

Compiled and linked as:Compiled and linked as: gcc one.cgcc one.c

run as:run as: ./a.out./a.out

9292

Compilation ProcessCompilation Process.c and .h

.o

a.out

.i

.s

gcc -E

gcc -S

gcc -c

.a ar

gcc -o

9393

A simple C programA simple C program

#include <stdio.h>#include <stdio.h>main(int argc, char* argv[]) {main(int argc, char* argv[]) { if (argc > 1)if (argc > 1) printf("hello %s\n", argv[1]);printf("hello %s\n", argv[1]); elseelse printf("hello world\n");printf("hello world\n");}}

command line argumentscommand line arguments

9494

A simple C programA simple C program

to compile:to compile:

gcc two.cgcc two.c

produces:produces: a.out a.out

oror

gcc -c two.cgcc -c two.c

produces:produces: two.o two.o

9595

A simple C functionA simple C function

#include <math.h>#include <math.h>

int compute(int x, int y) {int compute(int x, int y) { double tx = x, ty = y, tr;double tx = x, ty = y, tr; tr = pow(tx, ty);tr = pow(tx, ty); return (int) tr;return (int) tr;}}

uses math libraryuses math library

9696

Multiple source filesMultiple source files

9797

A main programA main program#include <stdio.h>#include <stdio.h>main() {main() { int x, y, p;int x, y, p; printf("This program computes x^y\n");printf("This program computes x^y\n"); printf("Enter x: ");printf("Enter x: "); scanf("%d", &x);scanf("%d", &x); printf("Enter y: ");printf("Enter y: "); scanf("%d", &y);scanf("%d", &y); p = compute(x, y);p = compute(x, y); printf("Result: %d\n", p);printf("Result: %d\n", p);}}

asks for user inputasks for user input

9898

Steps to create an executableSteps to create an executable


gcc –c compute.cgcc –c compute.c

gcc –c power.cgcc –c power.c

gcc compute.o power.o –lm –o powergcc compute.o power.o –lm –o power

to runto run

./power./power

9999

make utilitymake utility

has configuration file that specifies has configuration file that specifies dependencies: dependencies: makefilemakefile

checks timestamps on fileschecks timestamps on files

recompiles necessary filesrecompiles necessary files

100100

makefilemakefile

power: power.o compute.opower: power.o compute.o

gcc power.o compute.o -o power -lmgcc power.o compute.o -o power -lm

power.o: power.cpower.o: power.c

gcc -c power.cgcc -c power.c

compute.o: compute.ccompute.o: compute.c

gcc -c compute.cgcc -c compute.c

101101

C++ Programming in aC++ Programming in a

UNIX EnvironmentUNIX Environment

102102

Creating a C++ ProgramCreating a C++ Program#include <iostream>

main() { cout << "hello world" << endl;}

Stored as:Stored as: one.ccone.cc

Compiled and linked as:Compiled and linked as: g++ one.ccg++ one.cc

run as:run as: ./a.out./a.out

103103

A simple C++ programA simple C++ program

#include <iostream>#include <iostream>

main(int argc, char* argv[]) {main(int argc, char* argv[]) { if (argc > 1)if (argc > 1) cout << "hello " << argv[1] << endl;cout << "hello " << argv[1] << endl; elseelse cout << "hello world\n";cout << "hello world\n";}}

command line argumentscommand line arguments

104104

A simple C++ programA simple C++ program


g++ two.ccg++ two.cc

produces:produces: a.out a.out

oror

g++ -c two.ccg++ -c two.cc

produces:produces: two.o two.o

105105

C++ classesC++ classes

Class header and bodyClass header and body

Header in header fileHeader in header file .h.h

Body in body fileBody in body file .cc or .C.cc or .C– includes header fileincludes header file

main function still requiredmain function still required

106106

A simple C++ class headerA simple C++ class header

#ifndef COUNTER_H#ifndef COUNTER_H#define COUNTER_H#define COUNTER_Hclass Counter {class Counter { int value;int value; public:public: Counter();Counter(); void increment(int);void increment(int); void reset();void reset(); int getValue();int getValue();};};#endif#endif

107107

A simple C++ class bodyA simple C++ class body

#include "Counter.h"#include "Counter.h"

Counter::Counter() {Counter::Counter() { reset();reset();}}void Counter::increment(int n=1) {void Counter::increment(int n=1) { value += n;value += n;}}void Counter::reset() {void Counter::reset() { value = 0;value = 0;}}int Counter::getValue() {int Counter::getValue() { return value;return value;}}

108108

main C++ programmain C++ program

#include <iostream>#include <iostream>#include "Counter.h"#include "Counter.h"main() {main() { Counter c;Counter c; int value;int value; cout << "enter value: ";cout << "enter value: "; cin >> value;cin >> value; c.increment(value);c.increment(value); cout << "counter now: " cout << "counter now: " << c.getValue() << endl;<< c.getValue() << endl;}}

109109

makefilemakefile

count: Counter.o main.ocount: Counter.o main.o

g++ Counter.o main.o -o countg++ Counter.o main.o -o count

Counter.o: Counter.CCounter.o: Counter.C

g++ -c Counter.Cg++ -c Counter.C

main.o: main.Cmain.o: main.C

g++ -c main.Cg++ -c main.C

part one the essence of unix. 2 overview unix history –origins, versions, distributions using unix...

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