The UNIX Operating System

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TCS ConfidentialTCS Confidential

The UNIX Operating System

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UNIX Operating System

Objectives : Learn about the Unix Operating System and develop the skills

required to build software applications in the Unix Environment.

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1. Introduction & History of UNIX

2. File System

3. Basic Utilities

4. Shell Features

5. Advanced Utilities

6. Communication Features

7. System Calls

Contents :

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Chapter 1

Introduction and History of UNIX

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Introduction and History of UNIX

1. Evolution 2. Development 3. Standard release- AT&T versions 4. BSD UNIX 5. Other implementations of UNIX 6. Features of UNIX 7. UNIX Philosophy 8. UNIX operating system 9. UNIX Kernel 10. Programming Environment 11. Design Principles 12. Limitations

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Primarily influenced by MULTICS

MULTICS- Developed for GENERAL ELECTRIC 645

mainframe computer- Interactive operating system - Batch - mode characteristics

UNIX Operating System- First Version developed in 1969 by Ken Thompson on DEC PDP Series ( PDP - 7 )- Business, Scientific and Industrial Users

Evolution

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Development

* Originally written in assembly language for PDP-7

* Transportability facilitated by Thompson who developed the B language

* B language modified by Ritchie and renamed as C language

* Thompson (1980) and others wrote UNIX in C which could be ported to any computer

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Standard release - AT&T Versions

Version 3 • Written in C• Moved to PDP -

11/45 and PDP - 11/70

Version 6 • Released in 1975• For use by

universities onlyVersion 7 • Released in 1978

• First commercial version but primarly used in universities

• 32V - VAX version Version 8 • UNIX Support

Group(USG) takes responsibility

• Research Group still busy

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Standard release - AT&T Versions …Contd...

System III • Released in 1981• Commercial orientation• Over 100 manufacturers of UNIX-

based micro , mini and mainframes

• UNIX users > 100,000 System V Release 1 • Released in 1983

• Enhancement of System III System V Release 2 • Released in 1984

• Enhancements of System V , Release 1 System V Release 3 • Released in 1988

System V Release 4.0 •

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BSD UNIX (from Berkeley Software

Distributions) * UNIX's entry into University of California, Berkeley Campus during 1976-77 * Inputs of UCB Faculty/researchers incorporated in System V of AT&T UNIX

UNIX 3BSD • Released in 1978• Developed by Bill Joy and Ozalp Baboglu• Added Virtual memory, Demand paging

to the VAX version 32V

UNIX 4BSD • DARPA - funded Development• Provided support for DARPA TCP/IP• C-Shell , ex/vi , new compilers for PASCAL

and LISP were addedUNIX 4.1 BSD • Released in 1981

UNIX 4.2 BSD • Released in 1983

UNIX 4.3 BSD • Latest Release

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Other Implementations of UNIX (based on Version 7, System III, System V of AT&T UNIX or UNIX 4.2

BSD)

Xenix Microsoft’s UNIX operating system to run on microcomputers

IBM PC/IX IBM PCZeus Zilog ComputersDEC Ultrix DECHP-UX HPUNIX SUNElxsi UNIX ELXSIPyramid UNIX PyramidData General UNIX Data GeneralPerkin Elmer UNIX Perkin ElmerMassComp UNIX Mass ComputersNBI UNIX NBIAmdahl UNIX Amdahl

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Multitasking Performing tasks simultaneously rather than sequentially

e.g., While printing a document , start editing another document

Each task is considered to be a process

Multi-user Several users can use the same

computer simultaneously i.e , more than one

keyboard and terminal can be connected to one

computerHighly cost-effective

Portability Easier to modify the UNIX system code for installation on a

new computer rather than write from scratch a new operating

system

UNIX Features

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UNIX System supplied tools

Integral utilities Basic Operation of Operating system like Command

interpreter or Shell

Tools Text print formatting like nroff and typesetting troff

UNIX Features

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* Available on micros, minis and mainframes* UNIX Communication and electronic mail

• Communication between different terminals hooked to same computer• Communication between computers of different

sizes and types in different locations as far away

as other countries * Incorporation of third party application

programs * Hierarchical File System* On-Line Help facility

Example : man <Command> * Library of application software

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Make each program do one thing well Expect the output of one program to

become the input to another Suited for prototype development

i.e., design and build easily Modular approach

i.e., be prepared to throw and rebuild Usage of tools Building essential tools

The UNIX Philosophy

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Kernel Schedules tasks and manages data storage

Shell A program that • interprets the user commands/requests

• calls programs from memory and

• executes them one at a time or in a series

(called a pipe)

Tools & Specific capabilities added on to the OS

Applications

Kernel( Heart of Unix Operating System)

Shell Interpreter

Tools and Applications

The UNIX Operating System

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The UsersShells and Commands

Compilers and InterpretersSystem Libraries

System Call Interface to KernelSignal File System CPU

Scheduling

Terminal Swapping Page Handling

Replacement

Character Block Demand PagingI/O System I/O System

Terminal Disk & Tape VirtualDrivers Drivers Memory

Kernel Interface to the Hardware

Terminal Device MemoryController Controller Controller

Terminals Disks & Tapes Physical Memory

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File ManagementAnd SecurityNetworking

Services

Date and TimeServices

Input / OutputServices

SignalHandling

ProcessScheduling

SystemAdministrationand Accounting

MemoryManagement

UNIXUNIX

SYSTEMSYSTEM

KERNELKERNEL

The UNIX Kernel

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* A GOOD operating system !!

• Simple yet powerful• Allows building of tools, writing of small

programs and putting them together• A rich & productive environment

* A PORTABLE operating system !!• Written in C • Runs on a range of computers • Source code is available

The Programming Environment

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* Designed for Programmers* Interactive * Multiple Processes can be initiated

Foreground ProcessBackground Process

* Methods to Co-ordinate Process* Signal to communicate with processes* Files, Directories, Devices treated as files * Tree structured directories to hold files* Emphasis on program development facilities* Sources available on-line* Simplicity before efficiency

The Design Principles

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* Designed for computer professionals

* Not a real-time operating system

* File Security depends on owner

* Defective programs may keep running

Drawbacks of UNIX

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Chapter 2

File System

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1. File System Layout2. Concepts of file 3. Features of File system 4. Starting and Ending a session5. File Management utilities 6. Directory Management 7. File operation 8. Mountable File System9. File security

The UNIX File System

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Disks are partitioned into File Systems.- Logical blocks of 512 bytes or multiples- Arranged to form a hierarchical structure- Convenient to manage data

File System Layout

Boot Super Inode Datablock block list block

Boot block- generally occupies the first sector- may contain bootstrap code

Super block- Information about the file system

How large, where free and other detailsInode list

- Contains a list of inodes- One inode is the root inode

Data block- Contains file and administrative data- Allocated data can belong to that block

only

File Systems in UNIX

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- Ordinary Files

- Directory Files

- Special Files

- Standard Files

Classification of files in UNIX

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* A File in UNIX is a Stream of bytes ( 8-bits)Kernel does not impose a structure on files

* File may contain text, data and even machine language code

Examples Text Files : Lines of ASCII characters

separated by a new-line

Commands : Sequence of commands interpreted by UNIX text

Data : File containing data as

stream of bytes

Executable : File containing machine language instructions

* The files format remains unchanged but only the way the program interprets it is different

Concept of Ordinary Files

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* Gathering together related files in a common place

* Every file is assigned to a Directory

* Directories have names (maximum of 14 characters)

* A file within a Directory can itself be another Directory (A Sub-directory)

* Internally a Directory is just a file that contains - a list of file names

- their Inode Numbers and - a pointer to the actual file on the

disk

* An upper limit of around 35 sub -directories

Examples

/ ( Forward slash ) Prime or Root Directory Note - in DOS it is \

( Backward slash ) /usr Directory for the user

/usr/trg1 Sub-Directory for trg1 under Directory usr

Concept of Directory Files

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* Used to reference Physical devices such as terminals, disks, floppy drives and tape drives

* Read and written like ordinary files

* Requests cause activation of the associated Physical Device

* Device Drivers associated with each file

* Types :Character file Terminal (tty0, tty1 ) Transmits data Character by CharacterBlock file Disk Drives (hd0,fd0) Transmits data in 512 or 1024 byte chunks * Major and Minor numbers identify the hardware link

Major No.s : Indicates type of deviceMinor No.s : Different instances of the

device

Concept of Special Files

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* Helps display information on the screen* Special Names for Communication channels * Keyboard input channel is called Standard

input (stdin) - file id is 0

* Terminal Screen output is called Standard output (stdout) - file id is 1

• Diagnostic error messages (generated by a program) are sent to Standard error

(stderr) - file id is 2 ( shown on terminal screen )

* All three files are open by default at the time of login

Concept of Standard Files

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* A means for the system to identify a fileNote : Unix is case sensitive

* User accesses a file by a user-assigned file name * Can be a sequence of characters (a maximum of 14 )

* May be identified by two or more names (Multiple links to a file)

* Internally assigned a unique inode number (for a File System) * Different files can be grouped under a

directory

File Names

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Absolute Path name

* A file is identified by the path name from the roote.g.,

/usr/trg/c/test.cwhere

• test.c is an ordinary file• usr, trg, c are directories• trg is a sub-directory under usr

Relative path name

* UNIX keeps track of the user's current directory

* If a "/" does not precede a file name then the name interpretation

begins with the current directory e.g.,

If current directory is /usr/trg then the file could be just referenced as c/test.c

Path Names

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* Hierarchical

* Security on each file - Owner

- Group - All others

* Separate security for - read

- write and - execute

* Removable

* File Independence -

* Time stamp on each file - Modification time

- Access time

Features

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dev

bin

lib

spool

etc

tmp

consolelp0tty0

shcsh---

---Libc.a

groupinit---

passwd

/

spelltroff---

man

---

local

uch

bin

src

lib

tmp

---

---

troff

tmac

---

lib

bin

*.hincludeusr

Unix

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/bin Basic Unix utilities cp, mv, ln

/dev Special I/O device files fd0, lp0

/etc Administrative Programs passwd, shutdown

/lib Libraries used by Unix libc.a

/usr/bin Unix utilities cal, bc,spell

/usr/adm Administrative commands and files

adduser

/tmp Temporary files created on error conditions

Standard File Hierarchy

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/usr/games - Game Programs

/usr/include - Include files for language procedure

Examples : C-header files

stdio.h, math.h /usr/lib - Archive libraries

Example : troff

/usr/mail - Mail filesExample : mailbox

/usr/news - News files

/usr/spool - Spool files

/usr/tmp - Temporary files

/usr/src - Program Source Files

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* Three levels of accessUser/Owner, group, others

* Three types of access on Files and DirectoriesRead, Write, Execute

Access Mode Ordinary Directory

Read Examination of Listing ofFile Contents files within

Directory

Write Allows changing Creating newof file contents files within

Directory

Execute Executing file as Searching thea command Directory allowed

allowed

Security and Access Methods

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login : User can type his name and password to identify himself

login command can be used as $ exec login

to log-on onto another user account after identifying yourself in response to prompts for user name and password

su setuser

This is used to become another user or super-user provided the password is known.

e.g., $su

Prompt the user for the superuser password $su - trg2

Prompt the user for the password of user trg2 $su - trg2 -c "ls -l"

Temporarily changes to trg2 and executes the command ls -l and comes back to the original user

Starting and Ending a Session

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Starting And Ending A Session …Contd….

passwd Change the password for the usere.g., $ passwd

Prompt you for old password and new password

logout This command exits or logs-out from the current user

and executes the file .logout before coming out

e.g., $ logout or $ exit or $ <ctrl-d>

exits from the current login

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Directory Operation File Comp.SecurityManagement

cd cmp passwdpwd comm cryptmkdir chownrmdir chgrpmvdir umask

chmod

File File Mountable Copy, Movecontents compression file Remove & Time

cat pack mount cpls unpack umount lnwc mvfile rm

touch

File Management Utilities

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mkdir creates a new directory

rm removes a file

rmdir removes a directory

du displays disk usage

df displays number of free block

touch updates the time of last modification

find locates files that match certain area

file displays the type of file

pwd displays full pathname of current

directory

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General Structure:Command Name [Options] [Arguments]

E.g.,

Command NameTells the shell what to do(in this case list files)

OptionsControl how the command will work (in this case ask for a long listing)

Argumentson which the command works(in this case the directory usr/trg )

ls -l /usr/trg

Command Structure

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Directory Management

cd Change working Directorycd.. Parent Directorycd. Current Directory

e.g.,$ cd /usr/trg/c ( current Directory is c )$ cd .. ( current Directory is trg )$ cd ./c ( current Directory is again c ) or $ cd c$ cd ( home directory - in this case /usr/trg)

mkdir Make a Directory $ mkdir pathname

Makes Directory in 777 mode

Write permission should at least be permitted for owner in parent Directory

e.g.,$ mkdir /usr/trg2 ( makes directory trg2 )

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rmdir Remove a Directory$ rmdir pathname

* Directory should be empty, or elserm -r (recursively remove)

e.g.,$ rmdir /usr/trg2 (removes directory

trg2)

pwd Print Working

Directory

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cat Concatenate & Print on screen or printer$cat [Options] [Arguments]

Options - take input from stdin -n no. of output lines-s squeeze adj. blank lines-v enable display of non-printing

characters-b used with -n to avoid numbering

blank lines

e.g.,

$ cat try.c Display the contents of try.c on the screen

$ cat Takes input from stdin i.e. keyboard and displays on screen

File Contents

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$ cat f1 > f2 Takes input from file f1 & puts it

on file f2

$ cat f2 > f3 f3 contains the contents of f1

$ cat f4 >> f3 Appends the contents of f4 to

file f3

$ cat try[0-3] > final The file final contains contents of try0, try1, try2 try3

$ cat test* > report The file report contains all files beginning with test

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Is[Options] List the Directory Contents

Options -1 number one single column output

-l long format (II also used)

-a all entries including dot files

-s gives no. of disk blocks

-i inode no.

-t ordered by modification time recent

first recursively display all directories,

starting specified or current directory

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$ Is -I List the files along with the protection bits and the user

$ Is -a List the files starting with .and..also

$ Is -1 symtab.csymtab.otreegentest

$ Is -I -rw-r—r— 1 smj proj1 30766 Mar 3 15:08 symtab.c-rw-r—r— 1 smj proj1 8759 Mar 3 15:12 symtab.o-rwxr-xr-x 4 smj proj1 40743 Mar 3 15:23 treegendrwxrwxr-x 1 smj proj1 53 Mar 1 09:15 test

$ Is -a ....profile.cshrcsymtab.c...

$ Is -iI 10936-rw-r—r—I smj proj1 3076 Mar 3 15:08 test.c10936 - inode number of file test.c

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wc Word Count $wc [Options] filename

Options - Display no. of lines, words, characters

-I Display no. of lines-w Display no. of words-c Display no. of characters

e.g., $ wc test.c20 200 567820 - lines200 - words5678- characters

nl no. of lines in the file and temp’ly lists out the file

Similar to wc -l < filename >

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file Determine file types$file [Options] [Arguments]

Options -f filelistNormal File Types- C program text- assembler program text- commands text- ASCII text- English text

e.g., $ file test.cC Program test

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cp copy a file

-i - user interactive mode

e.g.,$ cp test.c test.c.baktest.c and test.c.bak contain the same

contentsExtra disk storage

In Create link

e.g.,

$ ln first.c second.cThe file is referenced by two different namesNo Extra disk storage

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mv Moves or renames files and directories

-i interactive modee.g.,

$ mv old.c new.cRenames the file old.c as new.c

rm Deletes the indicated file(s) files

rm removes files and directories-i remove interactively-f forcible remove-r remove recursively

• Dangerous• used in conjunction with -i

touch Updates access, modification or change times of a file

-a update access time-m update modification time-c prevents creating the file

e.g., $ touch f1* The current system date & time stamp is put on the file f1* If f1 does not exist then it is created with 0 bytes

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cmp Compare two files

If files are same no output is sent to the terminal, or else The line number and the byte at which the first difference occurs is reported

-s Outputs nothing Registers return code

Return code

0 if files are identical1 if files are different2 on error

e.g.,$ cmp test1 test2test1 and test2 differ in char 36 line 3$ cmp -s test1 test2$ echo $status

outputs 1 indicating that the files are different

File Comparison

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diff - Reports more than one differences

$diff [Options] file1 file2-b Ignores trailing blanks

-e Gives a list of ed commands so as to convert file1 into file2.

e.g.,$ diff test1 test2

Outputs: n1 a n3,n4n1,n2 d n3n1,n1 c n3,n4

where * n1 ,n2, n3 ,n4 are line numbers* a ,d, c means append, delete ,change

respectively

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comm Display common lines

$comm -[123] f1 f2 Prints a three column output:

- lines that occur only in f1- lines that occur only in f2- lines that occur in both

comm -12 - prints lines common to the two filescomm -23 - prints only lines in the first file but

not in the secondcomm -123 - prints nothing

e.g.,

$ comm test1 test2 Reports the common lines between files test1, test2 and

reports the lines differing

$ comm -12 test1 test2 Prints line common to both

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pack Compress the file

$ pack <filename>

e.g., $ pack try- Creates a file try.z which is packed- Normally the executables are packed- The size is reduced by 25 - 40 %

unpack Uncompress packed fileor pcat

e.g., $ unpack try.zor$ pcat try.z

unpacks the file try.z

File Compression

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mount Associates a directory with a device

e.g., Mounting a floppy on the root file system

umount Dissociates directory from the device

e.g.,$ mount /dev/fd096 /mnt Mounts the floppy on

the directory /mnt$ umount /mnt Dissociates /mnt from

the floppy

Mountable File System

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passwd To change the password

chown To change the ownership of the file

$ chown owner filename

e.g., $ chown trg2 test.c* Initially the owner is trg1* Only the owner or the superuser

can change the ownership of the file

File Security

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chmod change the permissions of the file

$ chmod who op permission <filelist>

who a, u, g, o all, user, group, others op +, -, = + add, - remove, = set permission r,w,x r read, w write, x execute

e.g.,$ chmod a=rw test.c

* users, group, others have read and write permissions

$ chmod u+r, g+w, o+x test.c* read for users write for groups execute for others

$ chmod 777 test.c* Sets read, write, execute Permissions

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umask Set file creation mode mask

$ umask nnn (nnn set file creation mode)umask can also be set as a shell variable

e.g., umask 022

- Files normally created with 777 mode is assigned 755 permission

The value of each digit is subtracted from the corresponding "digit" specified by the system for the creation of a file.

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tail Displays the last lines of fileoptions : -n (n= no. of lines)e.g., $ tail -30 test.cDisplays the last 30 lines of file test. c

head Displays the top lines of filee.g., $ head -10 test.c Displays the first 10 lines of

test.c

split Splits the file into different files as specified by the number of lines

e.g., $ split -20 test.c Splits the file test.c in blocks of 20 lines and creates files

xaa, xab, xac and so on, such thatxaa has first 20 lines of test.cxab has the next 20 lines of test.c

...The file test.c is unaffected$ split-20 test.c try Generates files as tryaa , tryab ,

tryac

paste Joins the two or more files horizontallye.g., $ paste xaa xab File xaa and xab are joined horizontally and output to

the terminal

File Operation

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Chapter 3Chapter 3

BASIC BASIC UTILITIESUTILITIES

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1. Line Editor Ed

2. Visual Editor Vi

3. Debuggers

4. Profiling Tools

5. C-Beautification

Basic Utilities

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Invoking ed: $ ed filename

Prompt :Ed has no formal promptP - Prompts with a “*” This is a toggle function

Append:a - Appends given text after current line

Write :w - Writing to the file

Exiting ed :q - Quit from ed

Example :

$ ed test.c? test.cP*a

<————> <————> <————>

*w*q

The edit buffer can be written to some other file also as *w filename

The Line Editor - ed

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abc abc

a*bc abc, aabc, aaa...bc

a.c abc, aac, acc, axc, a$c

a.*c abc, axyc, a$+pmc, abcdefgc

a[b2m]c abc, a2c, amc

a[0-2b-d]c a0c, a1c, a2c, abc, acc, adc

a[^0-2]c a3c, a5c, axc, ....

a[xy]*c ac, axc, axxc, ayyyc

a\{3,\} aaa, aaaa - 3 or more a’s

a\{3,5\} aaa, aaaa, aaaaa between 3 & 5 a’s

Pattern Matching

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Command Explanation Usage

p print current line (s) 1,3p

l list current line(s) 2,4l(display invisible characters

like tabs etc.)

n print line(s) with number before it 1,5n

a append text after current line 4a

i insert text before current line 3i

Adding and Replacing Text..

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Command Explanation Examples

. Pointer to current line * - Previous line

.= Gives line number

n Current line is ‘n’ * - Current line

+n Move up by n lines

-n Move down by n lines

$ points to the last line

, short for 1,$

; short for .,$

/.../ forward search for string of characters enclosed between slashes

*$= Prints total no. lines but does not changecurrent line

Traversing within a file

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Command ExplanationUsage

d delete line(s) in text 2,5d

c change line(s) in text 2,4c

m move line(s) in text 2,3m5

t copy line(s) in text 2,3t5

j join lines in text 2,3ju undo last command

Note : The above commands can be easily remembered by associating them with the first characters of their action.

Substitute Commands

(n,n)s/oldstr/newstr - replaces oldstr with newstr (n,n) range of lines - optional s/oldstr/newstr/g - all oldstrs' on the current line are replaced with newstr

s/oldstr/newstr/p - the replacement is only effected in print but not executed

s/oldstr/newstr&/ - newstr is inserted at every matchs/oldstr/%/ - matched strings are replaced by the

replacement string in the most recent substitute command

Modifying Text

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/^ pattern/ searches for patterns at beginning of line

/pattern $/ searches for pattern at end of line

/pattern/ the pattern is searched forward

// forward search

?? backward search

Finding Text

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Command Explanation

(n,n)g/findstr/commandlist Executes given commandlist for every occurrence of findstr

(n,n)G/findstr/ Inputs one command to execute for every occurrence of findstr

(n,n)v/findstr/commandlist Executes given commandlist for every non-occurrence of findstr

(n,n)V/findstr/ Inputs one command to execute for every non-occurrence of findstr

Command Execution

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Command Explanation

f print current filename

w write contents of buffer into file

w file2 write contents of buffer to file 2

r read current file after current line

r file2 read contents of file2 after current line

e file2 edit file2 —> invoke ed on file2

!shellcmd Execute shell command by preceding with ‘!’ ! ls –l gives a listing of current directory

Special ed Commands

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* an improved version of ed* less terse* provides display options like

numbered line

* allows shorthand versions of commands

* clear response for error messages

The ex editor

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The editor* Powerful full screen editor* vi v/s ed, ex* Mostly single key stroke

commands* Interface with ‘ex’* Macro facility* Ability to process text

Invoking $ vi filenamee.g., $ vi pgm.c

Modes :* Command mode* Insert mode

* From Insert mode Pressing <ESC> remitts Command mode

The vi - Visual Editor

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Types of commands* vi-commands (invisible)

Command mode

Commands can be categorised as :* Cursor movement* Text manipulations - insert, delete, copy, change* Marking/Selecting, Positioning* Search

Objects of interest recognized by ‘vi’:* characters* words* lines* block

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Format of commands[count] command [operand] Use “.” to repeat last commandUse “u” to undo last command

Cursor MovementLine Oriented :

^ or (zero) beginning of line$ end of line

Character orientedh move left

l move rightj move downk move up

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Format of commands (contd.)

Word Oriented :

e move to end of next word

w move to beginning of word

b move to beginning of previous word

E move to end of next word ignoring punctuation

W move to beginning of word ignoring punctuation

B move to previous word ignoring punctuation

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Block Oriented :

) move forward one sentence

( move backward one sentence

} move forward one para

{ move backward one para

% move to find matching parenthesisRightly used in C- Programming for

matching ‘(‘ & ‘)’

m mark a particular line with a label. e.g., ma (marks the line with label a)

“ return cursor to position (m)e.g., "a moves the cursor to the line

which was marked with label a

^g file information, line number

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Text Manipulation

Insert mode :a append after cursorA at end of linei insert at cursorI at beginning of lineo enter in new line after current lineO enter in before current lineesc to exit insert mode

Delete mode :u undo last commandnx delete n- next characterndw deleting n next wordsndd deleting n lines -

current line and n-1 below current line are deleted.

D delete till end of line

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Changing Text :

nr replace chars delete current char, enter

insert modeS delete line, enter insert

modecw change word

Cut & Paste :

nyy yank n lineNamed Buffers : a to z ( 26

)Unnamed Buffers : 1

p print buffer

Join :

J join next line to current EOL

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Search

Searching for a character :

fc search forward for character ‘c’

tc similar to f, cursor placed 1 char left of ‘c’

Fc search backward for character ‘c’

Tc similar to F, cursor place 1 char right of ‘c’

; continue search in same direction

‘ continue search in reverse direction

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Search

File Related :

G go to the end line

nG go to the nth line

M go to the middle line

H go to the top line

L go to the last line

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Text Manipulation

Screen Adjustments :

^d Scroll down half a screen

^u Scroll up half a screen

^f Page forward

^b Page backward

^e exposes one more line at bottom of screen

^y exposes one more line at the top of screen

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Text Manipulation

Searching for a string :

/string for searching forward

?string for searching backward

Use n to continue search in the same direction

Use N to continue search in the opposite direction

s/oldstr/newstr commands can be used in vi

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Common Set commands

set ai Causes automatic indentation

set noai Nullifies the effect of auto-indent

set nu Causes line numbers to be displayed

set wrapmargin = n Sets n column right margin

set bf The beautify option Removes all unimportant control characters

set Causes a displays of current set options

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Text Manipulation

:w! file force write

:q quit normally

:q! quit, no write

:n next file, for $ vi f1 f2 f3 f4

:n! edit next file, discarding changes to current file

:n args specify new argument list

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Why ?

* for running a Program under the control of the programmer * for examining the values of various variables and stack contents

Types

fsdb File System Debugger Fixes damaged file system

kdb Kernel DebuggerResides in kernel, Allows memory examination Disassembles instructionsExecutes programs

sdb - Debugging source code written in C, Fortran 77

- Available on System V

Role The functionality of any debugger is essentially the same

Debuggers :

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Debugger - sdb

* Invoked as

sdb <executable file>

e.g., $ cc -g test.c$ sdb a.out

* sdb checks for the status of files

* sdb gives warning messages if source files are not present or source files were modified after the object files

* sdb gives a prompt * after invocation

* some commands can be used to avail the important features of sdb

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SDB Commands

Command Explanation

*r <arguments> run the program (arguments optional )

*s stepping through the instructions*20b setting a break point at line number 20

(Normally break points are set at function calls)

*/pattern searches for the pattern*<function-name> b setting the break point at the function name\*B gives a list of break points\*d <line-no> deletes the break point at the specified line no.*D deletes all the break points

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sdb Commands (contd.)

Command Explanation

*S stepping over the function call

*c continue upto the break point

*variable name prints the value of variable active at that time

*variable name/x prints the value of variable in hex

*variable name/c prints the value of variable in character

*variable name/o prints the value of variable in octal

*variable name/s prints the value of variable in null terminated string

*variable name/a character strings at the specified address*function:variable prints the value of the variable in the

specified function

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sdb Commands (contd.)

Command Explanation

*p print the current line of the source

*<line-no>p print the corresponding line-no of the source

*<ctr-d> prints next 10 lines of source or data or instructions depending on the previous command

*w prints a window of 10 lines of source or data or instructions around the current line

*<Enter-key> executes the previous command

*!<command> executes the shell command

*k kills the debugger

*q quits the debugger

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CTRACE - Debugger

Different from the conventional debuggers like sdb

Works in the absence of a debugger

Ctrace simulates the insertion of printf statements

– Programmer’s way of debugging is to insert printf statements at the required places

– Results in more printf statements than the program itself

Ctrace also traces infinite loops

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CTRACE - Debugger (Contd .)

* Invoked as ctrace [options] < source-file > traced-

file

options :

-o print the variable in octal-x print the variable in hex

-u print the variable in unsigned format

-e print the variable in floating point format

-f <function-names> trace only the selected function names

-v <function-names> complement of option -f trace all functions except those specified in the list

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e.g.,

$ ctrace < test.c > ctest.c

test.c - source filectest.c - traced file

Compile the traced file as

$ cc ctest.c

creates in a default file a.out

Run the executable

$ a.out <arguments>

arguments are optional

Outputs the values of variables and statements as desired by the user

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PROF and GPROF

* Improves efficiency and debugging

* gprof is available in BSD versions

* The program should have been compiled with -p option for prof and -g option for gprof

* prof - refers default input file mon.out

* gprof - refers default input file gmon.out

* Gives an idea as to which function used up the maximum time

PROFILING TOOLS :

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Example of prof

$ cc -p test.c$ a.out$ prof a.out

Generates an output like....

%time cumsecs seconds #calls msec/call name91.2 9.34 9.34 20100 _func27.2 10.08 0.74 1 acnt1.0 10.18 0.10 100 _func1 0.0 10.24 0.06 1 _main

%time Percentage of time consumed by the function

cumsecs Running sum or cumulative sum of the functions called

seconds Seconds consumed by the function

calls Number of times the function was invoked

name Function name

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* Beautifies the C-program code

* Indents all the statements

* Improves readability

* Invoked as

$ cb < source-file > target-file

e.g.,

$ cb < test.c > test1.c

test.c - source file

test1.c - Beautified version of test.c

CB - C Beautification

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Chapter 4Chapter 4

Shell Features Shell Features

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Shell Features

1. Various kind of shells 2. Shell commands3. Shell Startup Dot files4. Shell variables5. C Shell6. Test conditions7. Shell programming - Bourne Shell8. Shell programming - C Shell

Shell Features

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1. Bourne Shell sh

2. C Shell csh

3. Korn Shell ksh

4. Restricted Shell rsh

5. Visual Shell vsh

Various types of Shells :

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Simple commands using shell Metacharacters

Exit status - return value 0 - Successful - return value > 0 - Failure

Redirection Default input from KeyboardDefault output on the Screen

< - Read from a file> - Redirect it to a file>> - Append to a file

n>&m - Merge output from file descriptor n with file descriptor m

n<&m - Merge input from file descriptor n with file descriptor m

where n and m are file descriptors for thestdin, stdout and stderr files

Pipeline sequence of commands separated by |

Shell Commands

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; sequential execution

& asynchronous execution

&& following list executed if preceding pipeline returns

zero value

|| following list executed if preceding pipeline returns nonzero value

* matches 0 or more characters

? matches any single character in filenames

$var value of shell variable var

var=variable assign variable to var

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# rest of the line is a comment

‘...‘ run command within backward quote

‘...’ treats ... literally

“...” treats ... literally except for $ and ‘...‘ and \

e.g.,

$ (sleep 5 ; echo “The date is `date` “ ) & date

The Output of the above command will be

6345

Wed Sep 23 10:20:45 EDT 1991$The date is Wed Sep 23 10:20:50 EDT 1991

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PATH

* If full path is given while executing the command, the command is executed from the path specified

* Else it is searched in the Shell variable $PATH

* Search order is defined by value of Shell variable Path

e.g.,

PATH = :.:/usr/bin:/bin:

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Shell Startup Dot files

* Helps in customizing UNIX System

* Executes .profile for Bourne Shell when user logs on

* Executes .login and .cshrc for C Shell when user logs on

* Executes .logout for C Shell when user logs out from C-Shell

* Keeps track of the history mechanism In C Shell through the .history

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Shell Variables

User defined assignment : name = value

e.g., (on Bourne shell)

$ x=”Hello how are you”$ echo $x

Hello how are you

$ PATH=$PATH:/usr/games$ export PATH $ echo $PATH

:.:/usr/bin:/bin:/usr/games:

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Positional Parameters

e.g.,

shellscript arg1 arg2

$0 $1 $2

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Evaluation of Shell Variables

* $var value of var ; nothing if undefined

* ${var} same as $var ; useful if alphanumeric characters

follow variable name - derefrencing variable

e.g.,

$ var=hello

$ varx=goodbye

$ echo $var

hello

$ echo $varx

goodbye

$ echo ${var}x

hellox

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* $ {var?message} If defined , $varOtherwise print messageif message not defined printdefault message

e.g.,$ echo ${var?}

hello

$ echo ${junk?}junk : parameter not set

$ echo ${junk?my message error}junk : my message error

* ${var-thing} Value of var if defined , else use thing$var unaffected

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* ${var=thing} Value of var if defined ; otherwise thing $var is set to thing

e.g., $ echo $ {junk-’Hi there’}

Hi there

$ echo ${junk?}junk : parameter not set

$ echo $ {junk=’Hi there’}Hi there

$ echo ${junk?}Hi there

* $ {var+thing} If var defined then thing Otherwise nothing

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Command Environment

* Variables & associated values

e.g., export A

* Export from parent to child shell

* Vice-versa not true

Shell 1

Shell 2

Export A

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Predefined Special Parameters

$# number of positional parameters

$? exit value of last command

$$ process number of a process

$* all the parameters

$! process id of last command started with asynchronous execution i.e., &

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Variables Used by Bourne Shell in .profile

CDPATH search path for cd

HOME login dir

PATH search path for commands

PS1 primary system prompt

PS2 secondary system prompt

IFS internal field separator

MAIL files containing mail messages

TERM terminal type

EXINIT list of set commands for vi

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* Developed by Bill Joy ( Berkeley University)

* More helpful interaction

* Permits shorthand repetition

* Permits aliasing

The C Shell

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The variables can be defined using a set for C-Shell variables

e.g., (on - C shell)

% set x=‘date‘% echo $x Wed Sep 23 12:15:20 EDT 1991

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History - Records previous commands ! is used to execute previous command

Command Format :! <event> [ <word> <modifier> ]

<event> - absolute !1- relative !-3- name !c expr !?su?

<word> - absolute 0, 1, ...n- range a - e- last $ - All arguments *

<modifier> - Substitute :s/trg1/trg

- Print only :s/trg1/trg/p

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History Mechanism

Keeps track of commands

% history Lists previous commands

% ^old^new Modify last command

e.g., % cd /usr/trg/SRC

% ^SRC^src

% cd /usr/trg/src

% !15 Run command 15

% !c Run previous command beginning with c

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Changing Commands

:S/pattern/replacement

e.g.,

% !cd:s/trg/trg1

cd /usr/trg1/src

% !ls : p Prints the previous command beginning with ls but does not execute it

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Using Arguments

!$ last argument

!^ Begin argument

!* All arguments

!10:5-9 Arguments 5 to 9 for command 10

e.g.,

%ls !15:2-4

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Alias mechanism

Short names for frequently-used long commands

e.g.,

% alias cdms ‘cd /usr/man/man\!$’% cdms 2% pwd

/usr/man/man2

% alias cd ‘cd \!*;set prompt=”`pwd`>”’sets the prompt to the present working directory as and when cd is used to change the working directory.

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{ } Attach filenames to common root

%cp /usr/trg4/{ac,docs,test} .

%cp/usr/trg4/ac .

%cp /usr/trg4/docs .

%cp /usr/trg4/test .

%ls {/usr/bin,/bin}/{ls,more}

/usr/bin/ls : not found

/bin/ls

/usr/bin/more

/bin/more : not found

Filename Grouping

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Using C - Shell e.g.,

% cc test.c% vi test.c% !c% a.out% !v% !c - o test% test% car /usr/trg2/document/report

% !! : s/car/cator

% ^car ^cat

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Variables in .cshrc of C SHELL

% set variable=value

histchars :% set histchars=";,"will thereafter use

; as execution character , as substitution characterhistory :% set history=40

path:% set path=:.:/bin:/usr/bin:

prompt :% set prompt=”\!>”

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Variables in .cshrc of C SHELL

setenv used to make a variable as an environment variable so that whenever changes are made it is also reflected in the environment like TERM , DISPLAY is used

% setenv TERM=AT386-M

filec : file name completion% set filec : Predefined Its usage : % set variable

% unset variable

ignoreeof : To ignore all eof character ^D% set ignoreeof

noclobber : Abandons all command using output redirection % set noclobber which destroys an existing file and appends to non-existing file

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TESTing Strings

test - z $string String length equal to zero

test - n $string String length not equal to zero

test $str1 = $str2 str1 is equal to str2

test $str1 != $str2 str1 is not equal to str2

test $string string is not a null string

Test Conditions

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To algebraically compare variable values

test $num1 -eq $num2

Other algebraic operators -ne, -gt -ge -lt, -le

File related

$ test -f file True if file exists and is an ordinary file

$ test -r file True if file exists and is readable file

$ test -w file True if file exists and is writable file

$ test -s file True if file exists and has size greater than zero

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Control flows

if command thencommands [ elif commands ] ...[ else commands ]fi

case word in,pattern) commands ;;pattern) commands ;;...esac

Shell Programming - The Bourne Shell

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for name [ in word ...]do

commands done

while commanddo

commands done

until commanddo

commands done

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break n exit from for / while / until from level n

continue n next iteration of for / while / until from level n

exit n exit with value

export [name..] export

test expr evaluate conditions

read [arg] read variables from stdin or Keyboard

shift n shift positioned parameters w.r.t $1

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Examples $ for i in *.dat> do > size=‘wc -c $i‘ > if test $size -eq 0> then> rm $i> fi> done

- The complete for loop can also be edited in a file and, by granting the

execute permission on the file , the Shell program can be invoked

- By default any shell program is parsed to Bourne shell

However, by mentioning #! /bin/sh or #! /bin/csh in the first line of the

shell program, it can be parsed to either Bourne shell or C-shell resp’ly

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Exampleecho If you have a TTY vt100 enter vt100echo If you have a TTY AT386-M enter AT386-Mecho If you have a TTY sma84 enter sma84read termcase $term in

vt1001) TERM=vt100;;

AT386-M) TERM=AT386-M;;

sma84) TERM=sma84;;

*) echo ‘Invalid TERM’;;

esac# Making it is an environment variableexport TERMecho end of program This can be a part of your .profile

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Control Flows

IF if (expr) thencommand;

[ else if ]command;

[ else ]command;

endif

SWITCH switch (string)

case string1:command;

breaksw

case string2:command;

breaksw

default :command;

breaksw

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FOREACH foreach name (word)

commands end

WHILE while ( expr ) commands

end

UNTIL until ( expr )commands

end

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Chapter 5Chapter 5

Advanced UtilitiesAdvanced Utilities

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1. Redirection2. Pipes3. Pipe fitting with tee utility4. Filters5. Find6. Sort7. Utilities that process tabular data-

cut, join, csplit 8. Ps and Kill9. Timely Execution- nohup, at, time 10. User backup utilities- tar, cpio, dd ,

doscp 11. Output related commands- pr,

lpr,lp 12. Other utilities- sleep, sync, wait,

clear, tr 13. Introduction to Make14. Lint15. Lex 16. Yacc

Advanced Utilities

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Redirection Metacharacter Performs

“<“ input

“>” output write

“>>” output append

e.g.,$ whotrg1 tty00 Apr 8 09:33trg2 tty02 Apr 8 11:10

$ who > who_out

$ cat who_outtrg1 tty00 Apr 8 09:33trg2 tty02 Apr 8 11:10

$ date > date_out

$ cat date_out Fri Apr 8 14 : 30 : 10 est 1983

$ who >> date_out$ cat date_outFri Apr 8 14 : 30 : 10 est 1983trg1 tty00 Apr 8 09:33trg2 tty02 Apr 8 11:10

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Metacharacter Performs

“|” piping

e.g.,

Without Pipe $ cat /etc/passwd > temp$ sort < temp$ rm temp

With Pipe $ cat /etc/passwd | sort

* No need for creation/deletion of a file

* Sorts the file passwd as per the first entry in passwd

Pipes :

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A UNIX Pipeline

Standard Input

>Prgm #1 Prgm #2 Prgm #3 Prgm #4

>Prgm #5 Prgm #6

Standard Output<

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Helps in creating the intermediate file during the pipe operation

e.g.,

$ ls *.c | tee Cflst | sort$ cat cflst

* Creates the intermediate file Cflst * Cflst contains the list of c files

The TEE Utility :

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grep get regular expressions only

fgrep fast, several simple strings at one time

egrep extended grep, can handle more powerful expressions like | - or operators

FILTERS :

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$ grep pattern filenames

Options :

-c number of lines matched

-i ignore case

-n print line with line-number

-v print lines which do not match

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Searching Files with grep

e.g.,

$ grep -ni func1 *.c Prints all the lines and line numbers in files *.c

that match pattern func1 ignoring the case

$ grep ‘*’ * Search for the pattern * in all the files

$ ls -l | grep ‘^d’ Searches for all subdirectories

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e.g.,

$ egrep ‘int|long’ test.c Searches for all those lines containing

either int or long in test.c

$ egrep ‘ (^[A-Z])’ testfile Searches for all the lines which start with a capital letter

$ cat exprfile Searches for lines having at least 3 commas ,.*,.*, in file testfile using the

exprfile

$ egrep -n -f exprfile testfile

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Find To locate one or more files

find path-list cond-list action-list

path-list one or more directory namescond-list -type x x can be d, f, or c

d directoryf ordinary filec character special file

-user name for a specificed user name

-group name for a specified group name

-size n File size n. blocksIf n follows c then so many characters

-links n locate for file with n links

-atime n files accessed during n days ago

-mtime n modified n days ago

-ctime n created n days ago

-perm nnn permission flags match nnn

-name fname with specified filenames

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actionlist

- print display path names

- exec command execute the unix command

- cpio device copy the files on the tape in specified format

- ok command like exec , but executed interactively

e.g.,find / -atime 7 -print - will print files accessed in

exactly 7 daysfind / -atime +7 -print - will print files accessed

earlier than 7 daysfind / -atime -7 -print - will print files accessed

within 7 days

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Examples

$ find / -atime +30 -print

$ find / -atime +30 -size +10 -print

$ find / -atime +30 -size +10 -ok rm -f {} \;

$ find . -perm 0777 -print

$ find . -perm 0777 -print -exec rm {} \;

$ find / -name passwd -print

- Will find the passwd file

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Sort* Sort keys can be fields or lines* A field is a string of characters separated by a field separator or new line.

$ sort {-options} {+post1} {-post2} {files}

The sort key begins at post1 ands ends just before post2. There can be several keys.

Options b ignore leading blanks and tabs

c only check if input file is already sorted

d dictionary order letters, digits, blanks

f ignore case

i ignore non-printable characters

n numeric sortingr reverse ordertp use p as separatoru output only lines with unique keyso filenameout save output in filenameout

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e.g.,

$ sort -t: +2n -3 /etc/passwd

Print the passwd file sorted by numeric user id

$ who | sort +4n

Sorts according to the login time stamp of the user

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uniq Finds and eliminates duplicate lines in a file and is often used with sort

$ sort <file> | uniq -c

Sorts and ouputs the number of count of lines containing unique fields

$ sort <file> | uniq -d

Gives only the duplicated lines

tsort Accepts as input a partial ordering and produces a fully ordered list of the items.

$ tsort psortfile

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Cut

* Deletes columns from a file producing a new file with shorter lines

* Cuts out selected fields of each line in a file.

* Cuts columns from a table or fields from a file which can be of type

- Fixed length fields or- Delimited by some character

Processing Tabular Data

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Cut (contd.)

cut -c list { file1 file2 ...}

e.g.,

cut -c 5-70 file1

cut would pass 5-70 characters from file1

cut -flist {-d char } {file1 file2....}

e.g.,

who | cut -d” “ -f1

gives a list of user login names

cut -d: -f 1,5 /etc/passwd

gives a list of user ID and names

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JOIN

* Combines corresponding lines in two files by relating the contents of one or more columns.

* Implements a relational data base ‘join’ on two tabular files

-jn m join on the mth field of file ‘n’

-on.m output mth field of nth filen - file no. m - field no.

-tc use char c’ as separator

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e.g.,

$ join -j1 4 -j2 3 -o 1.1 2.1 1.6 -t: etc/passwd etc/group

- joins field group id

- outputs the following parameters

login group loginname name dir

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csplit context split

$ csplit [-k] [-f prefix] [-s] file name arg1 [..argn]

Reads file and separates it into n+1 section defined by arg1...argn

Options :

-s Normally csplit prints the character counts for each file , -s is to suppress this

-k csplit removes previously created files in case of error , -k is to avoid this

csplit normally creates file as xx00 , xx01 ... , xx99

-f prefix creates file with that prefix instead of default xx

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csplit(contd.)

e.g.,

$ csplit -f cobol inpfile /Procedure division/’ / Para5./ /Para6./ /Para 7./

* Creates file as cobol 00 .. cobol 03* Edit these Cobol files* Can be recombined as

$ cat cobol 0[0-3] > file

csplit -k prog.c ‘%main(%’ ‘/^}/+1’ {20}

* Breaks file prog.c containing C routineupto a maximum of 21

* ‘% expr %’ —> no. file is created for this section

* No csplit for the main routine ‘%main%’

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PS, kill

$ somecommand &

5511 - pid

$ps

pid tty time command

3432 2 0 : 24 -sh5765 2 0 : 03 ps5511 2 0 : 51 somecommand

$ kill 5511$ pspid tty time command

3432 2 0 : 24 -sh5985 2 0 : 03 ps

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$ stubborn-cmd &

pid tty time command3432 2 0 : 24 -sh6004 2 0 : 03 ps5995 2 0 : 44 stubborn-cmd

$ kill 5995

$ ps pid tty time command3432 2 0 : 24 -sh6004 2 0 : 03 ps5995 2 0 : 44 stubborn-cmd

$ kill -9 5995

$ pspid tty time command3432 2 0 : 24 -sh6103 2 0 : 03 ps

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time Time a command

$ time wc test.c > wc.test real 2.0user 0.4sys 0.3

nohup Protecting a process from hanging and quit signals or interrupts

The standard output is sent to nohup.oute.g.,

$ nohup du / & 820 Sending output to nohup.out $ logout

Timely Execution :

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nice * Executes at specified priority* Default priority is 24

$ nice +n Raise priority

$ nice -n Lower priority

$ nice n set priority

at Executes process at specified time

$ at 5 pm echo ^G ^G Time to logoff >/dev/tty04 ^D

$

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tar tape archiver

Copies files on backup medium such as floppy or tape in tar format

tar [options] devicename filelist

Options :

c create a new tape backup tape old files are overwrittenr append files to the tape

t list the names of files from backup tapex extract files from the backup medium

u update a tape, if the named files are not present or have been modified later on

v verbose ; provides informational messages, such as the name of each file as and when it is

encountered

f devicename use device for backup medium

User Backup Utilities :

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tar (example)

$ tar cvf /dev/fd096 * copies all files from the current directory onto the backup medium /dev/fd096

$ tar xvf /dev/fd096 Extracts all the files from the backup medium /dev/fd096 onto the current directory

Creates necessary directories

tar xvf /dev/fd096 try.c Extracts the file try.c from /dev/fd096

tar tvf /dev/fd096 Generates a file list of /dev/fd096

find / -mtime -7 -exec tar uf /dev/fd096 {} \; All the files modified last week is backed up onto /dev/fd096

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cpio * Copy files archives in and out* Bundles all the files into one package

cpio [options] file list devicename Options

-o Copy these files onto tap

-i Extract files from tape

-p Read a list of file or path names from the standard input

-v display a verbose set of cpio action

-c character information in ASCII for portability considerations

-t For listing files from the backup medium

-O Append files to the end of tape to be used with -A

-d Creates necessary directories

-k In case of error , ignore the error and continue

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cpio (Examples)

$ ls *.c | cpio -ocBv > /dev/rmt/0n

Lists the files *.c and copy onto the device /dev/rmt/0n

$ cpio -ocBv < filelst > /dev/rct/c0s0

Copies all the files mentioned in filelst onto the catridge tape

$ cpio -icBdv < /dev/rct/c0s0

Extracts all the files from device c0s0 and creates necessary required directories

$ cpio -itv < /dev/rmt/0m

List the files from the tape /dev/rmt/0m

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dd convert, reblock, translate, copy a tape file.

dd {option = value }

Options Values

if input file nameof output file nameibs input block size (Default 512)obs output block size(Default 512)cbs conversion block sizeskip n records before copying from I/P fileseek write after n output records in O/P filecount n records conv To ASCII, EBCDIC, lcase, ucase (separated by

a comma)e.g., $ dd if=/dev/rmt/0n of=x ibs=800 cbs=80 conv=ascii,lcase

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doscp Copy a UNIX file in DOS format orCopy a DOS file in UNIX format

doscp source file target file

e.g.,

$ doscp /usr/trg/test.c a: copies the file test.c onto the floppy

$ doscp a:try.c . copies the file try.c from the floppy onto

the current working directory

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pr prepares a file for printing

Options

-k K col. Output

+k from page k

-lk set length of page to k lines

-p pause after each page

-h take next argument as header

-wk set width to k characters

-d double space

e.g.,

$ pr -3 d h “file list” f1 f2- Generates a header as file list- 3 Column output- Double spacing

$ pr -5 wordlist - Generates 5 column output

Output Related Commands :

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pr (contd.)

$ pr myfileprepare myfilenov 24 : 11 : 31 1987 myfile page 1

$ pr -t myfile suppresses the header

This file can be printed using$ pr myfile | lpr

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lpr Print a file on the line printer

$ lpr myfile prints myfile on the printer

$ lpr -c myfile make a copy to the spool directory

$ lpr -r myfile myfile is removed from the spool

lp Combines the actions of pr and lpr

$ lp myfile prints myfile with header, date, time and page numbering.

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sleep Suspend execution

$ sleep 5 prompt appears after 5 seconds

$ sync * updates super block* writes all disc buffers* calls sync before stopping system to

ensure file system integrity* saves all modifications

$ wait waits till all background jobs are over$du determines disk usage

-s total blocks -a size of each file

Other Utilities

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df displays no. of free blocksdf [option] file system

clear clears the screen and the prompt goes to

top of screen

tr replaces specified characters with other characters

e.g.,$ tr “[a-z]” “[A-Z]” < lfile > ufileReplaces all small case letters to upper case letters

$ tr -d’ ‘ < tstfl > tstfl2Deletes all the blank characters

$ tr -s ‘\012’ < try > try2Removes adjacent blank lines in file try

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Making & Maintaining large programs

What is make? Program for maintaining large number of programs

Need for make * Difficulties in remembering the dependencies

* Simple mechanism for maintaining an up-to-date version of Programs

Characteristics * Helps maintain large systems

* Specifies dependencies of files in the system and t the actions to make them

* Uses creation date to determine the actions to be taken

make - An Introduction

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make : AN INTRODUCTION …Contd...

make program takes the file named makefile or Makefile as its input.

makefile details: - the names of the files that make up the program system- their interdependencies- how to regenerate the program system

Example :

final

mod1 mod2 mod3

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make : AN INTRODUCTION …Contd...

Example (contd):

Makefile or makefile

final : mod1.o mod2.o mod3.o cc -o final mod1.o mod2.o mod3.o

mod1.o : mod1.ccc -c mod1.c



Run the command as ....

$ make final

use -f urflname option If the name of the file is not Makefile or makefile

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Using the Macro facility and Inference rules

QSRC = qp1.c qp2.c qp3.cINCLUDES = lim.h com.hOBJECTIF = qp.o qex.o libs.a

query : $(OBJECTIF) cc -o query $ (OBJECTIF)

qp.o : $ (QSRC)cc -o qp.o $ (QSRC)

libs.a : libs(lib1.o) libs(lib2.o)qex.o lib1.o lib2.o : $ (INCLUDES)LIBES = libs(libs1.o) libs(libs2.o)prog : $(OBJECTIF) cc $(OBJECTIF) $(LIBES) -o prog

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* Reports the various inconsistencies that can exist in a program in the

following areas . Syntax errors. Unused variables. Unused arguments. Unused functions. Unused return values. Unused external variables. Unintialized variables. Type checking features. Portability considerations. Statement not reached. Excludes goto statements

* Invoked aslint [options] filename

Lint - C Program Checker

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Lint - C Program Checker …Contd...

Example :

test.c

#include <stdio.h>main(argc,argv)int argc;char **argv;{

int i,j,k,l,number,num2;int int1, int2; int arr[20];scanf(“ %d”,num2); printf(“The square root of %d is %f \n”,number , sqrt(number) );

i=arr[j++];add(int1,int2); }

add (int1,int2,res)int int1,int2, *res;{

printf("The value %d", int 1 + int 2);}

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Lint - C Program Checker …Contd...

Generate an output after invoking lint as lint test.c -lm

test.c warning : k , l unused in function main

warning : j may be used before set

warning : main() returns random to invocation environment

Function argument (number) type inconsistencyscanf (arg2) int :: format int * : test.c

Value type declared inconsistentlysqrt llib-lm : test.c

Function argument ( number ) used inconsistently sqrt ( arg1 ) : test.c

Function called with variable number of argumentsadd : test.c

Function returns value which is always ignoredprintf scanf

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source * General tool for separating character strings patterns in an input

* String patterns can be specified using rules

syntax definitions

% %

rules

% %

user subroutines

Lex

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Lex …Contd...

Example (on rule)

Expression ——> integer * integer

Expression ——> integer + integer

Expression ——> integer - integer

Expression ——> integer / integer

The lex specification file

%%[0-9]+ { return (INT); }[-*+/] { return (OPR); }[\t ] ;

{printf(“Lexical analyser error\n”);exit(-1);}

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Lex …Contd...

%%yywrap(){return(1);}

yywrap() indicates no further input available

Invoked as

$ lex filename$ lex lex.l

Generates

lex.yy.c

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What is it? Yet Another Compiler Compiler

Features * General tool describing input to a program

* Specify input structure

* Code for each structure

* Outputs a subroutine which handles the input

* User supplied routine to supply next basic item

Yacc :

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Yacc …Contd...

Specifications Declarations

%%rules%%

Example

%token INT OPR%start expr %%expr : INT OPR INT{printf(“The input expression is correct\n”);}| error{printf (“The input expression is wrong \n”);}%%

Invoked as $ yacc filename$ yacc yac.y

Generates y.tab.c

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Consider this program...

#include <stdio.h>main()

{yyparse(); }

#include “y.tab.c”#include “lex.yy.c”

The whole program can be compiled as ...

$ cc main.c -ll -ly-ll and -ly to link lex and yacc library$ a.out

A Program using both lex & yacc

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Chapter 6Chapter 6

Communication Features Communication Features

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1. User communication commandsmailwritetalkpostnewsmesg

2. Networking commandsuucpuutorlogintelnetftprcpuuxctcu

Communication Features

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* Mail

* Write

* Talk

* Post

* News

* Mesg

User Communication Commands :

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Mail Sends and receives mail messages between users

Sending mail on local system

At the end of the message press ^D to exit

$ mail <loginnames>

Example : (Assume the current user is trg)

$ mail trg1

Sending mail on remote system

$ mail recipient@remote_system.domain_info

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Receiving mail

$ mail Shows the message received

? Promptq quits [file] save (defalut mbox)w [file] write without headerd deleten or + next message- previousr reply to the senderm [user] mail to user! cmd run the shell command

* The message could be saved or deleted

* Environment could be setup in .mailrc

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User Communication commands …Contd...

Write Allows sending messages to a user terminal from

another terminal

The message is ended by pressing ^D.

$ write <username>

Talk Allows interactive dialogue between users at two

different terminals.

$ talk <username>

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Post Messages can be posted on a “bulletin board” for previewing by all users.

News * Keeps the user informed of current events* Refers file /usr/news

e.g., $ news Prints all the news , latest first

$ news reorg Prints the news named reorg

mesg The terminal can be write protected to prevent other users from

writing onto your terminal

e.g., $ mesg [option]option :- y write allowed

- n remove write permission on the terminal

$ mesg prints the current status whether mesg is y or n

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* uucp

* uuto

* telnet

* rlogin

* ftp

* rcp

* uux

* ct

* cu

Networking Commands

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uucp * allows copying files from one unix system to

another* Refers file uuname and uulog

uucp [options] source-files destination files

options -d make necessary directory-c do not copy local file to spool directory-m send mail to the requester when the copy is completed

$ uucp -d -m file? sys_2!/usr/spool/uucppublic

Copies the files file? creating appropriate directories onto system sys_2 onto

/usr/spool/uucppublic

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uuto * Simplified version of uucp* Sends file to /usr/spool/uucppublic

$ uuto filename(s) system!login

$ uuto -m test.c sys2!trg2

Sends a mail to the sender when the job is over

rlogin * Allows remote login over the network * Similar to telnet, but a much more flexible

facility.$ rlogin system_name!username

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Networking Commands …Contd...

ftp * File transfer protocol* Transfers files from one system to another

$ ftp

ftp > open sys1 Name login:passwd

ftp > ? Gives you the help

ftp > get filename Gets the file onto the current system

ftp > put filename Puts the file onto the \sys1

ftp > close $

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rcp Similar to ftp, but a much more flexible facility

uux * Unix to Unix command execution on remote

systems* Gather files from various computers, run a command on a specified computer and

redirect the stdout to a file on a specified computer

$ uux [options] commandstring All shell special characters must be quoted

$ pr minutes | uux -p host!lp

Command line queues the file minutes to be printed on the area of the computer host

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ct * Connect terminal to remote terminal* Connects your terminal to remote

terminal which is equipped with a modem

This command dials the phone number of the modem

$ ct [options] telno

$ ct -h -w5 -s1200 9=5553497

ct will call modem using a dialer operating at a speed of 1200 baud , wait for 5 minutes before quitting if dialer is not

available and use the -h option not to disconnect the local terminal

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cu * connects local system to remote system* allows you to be logged on to both

simultaneously

Examples cu -s2400 9=5557867 Connected

login :

~%take proposal Takes proposal from remote computer to local computer

~%put minutes minutes.bak Vice versa of take and puts the file minutes on the remote computer as minutes.bak

~%!comma run the command on local system

~%$command run the command on local and send the output to the remote terminal

~ % . terminate the link

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Chapter 7Chapter 7

System callsSystem calls

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1. Introduction

2. File related system callsopen()read()write()creat()chmod()chown()lseek()

3. Process related system callsfork()getpid(), getppid(), getpgrp()wait()execl()

System Calls :

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* Library functions and system calls

* Both are C - functions

* Difference lies in their incorporation in the UNIX System

* Library functions are referred to as add-ons

* System calls are part of the UNIX Kernel

* Library functions themselves use system calls and can be

expanded by the user

* System Calls generally common across UNIX versions * System calls share the concept of fd -file descriptor

* File descriptor is an integer used to identify a file

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Basic tasks in file operations

- opening files- reading files- writing in files- creating files- changing the permission of files - changing the owner and group of files- seeking to file-location - closing files

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open () * open() an existing file

int open (filename,mode)char *filename;int mode;

filename - character pointer to the name of the file

mode - integer signifying the mode0 for read1 for write2 for read and write

open() returns the file descriptors on success and returns -1 on error

Example :

Opening the file “test” in read mode and checking for the error condition

fd = open(“/usr/trg/test”,0);if ( fd == -1 ){

printf(“error in opening file test”);exit(1);

}

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read () * File should be opened in read mode

* read() an opened fileint read (filedesc,buffer,nbytes)

int filedesc;char *buffer;int nbytes;

filedesc - File descriptor indicating which file to be read

buffer - An area of buffer storage for holding the Characters read

nbytes - number of characters to be read at a time

read() returns the number of characters read and 0 in case ofend of file (EOF) and returns -1 on error

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Example :

Reading the file “test” 100 characters at a time

while ( ( n = read(fd,buff,100)) > 0 ){

printf(“file test has contents %s “,buff);}if ( n == 0 )

printf ( “ End of file “);

if ( n == -1 )printf (“Error in reading file test”);

When each read is finished the pointer advances by 100 bytes so that the next read picks from there

* If the number of characters left are less than nbytes ( in this example - 100 ) then read() will pick up what is left over

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write ()

* File should be opened in write mode

* write() to an opened file

int write (filedesc, buffer, nbytes)

int filedesc;char *buffer;int nbytes;

filedesc - File descriptor indicating which file to be written

buffer - The function takes from buffer and writes them to indicated file

nbytes - number of characters to be written at a time

write() returns the number of characters written and returns -1 on error

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Example :

while ( ( n = read (fd,buff,100)) > 0 ){

n1 = write (1,buff,100);/* writing to standard output *//* file id - 1 is for stdout */

if ( n1 == -1 )printf (“Error in writing on stdout");

}

if ( n == -1 )

printf (“Error in reading file test ");

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creat ()

* creat() creates a new file or overwrites on the existing file

int creat(filename, mode)char *filename;int mode;


mode - Integer signifying the modeThe mode is specified in octal code

creat returns the file descriptor on success and returns -1 on error

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creat () …Contd...

Example :

umask(0000);

fd = creat(“newfile”,0666);

if ( fd == -1 ){

printf(“error in creating file newfile “);

}

Creates a file called “newfile” in mode 0666 i.e., read and write permissions for owner, group, and others

Note : while creating a new file ensure umask is set to zero

Otherwise,

If umask had been 0022 in the environment variable, then the effective permission would be

mode & ~0022

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chmod ()

* chmod() set permissions for the file

int chmod (filename, mode)char *filename;int mode;


mode - Integer signifying the modeThe mode is specified in octal code

chmod() returns 0 on success

and returns -1 on error

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Example :

ret = chmod(“test.c”,0600);

if ( ret == -1 ){

printf(“error in changing the file permission”);

}

Changes the permission of file test.c i.e., read and write permissions for owner

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chown ()

* System call chown()

* chown() set ownership for the file

int chown (filename,owner ,group)char *filename;int owner , group ;

filename - character pointer to the name of the fileowner - owner id

group - group idchown() returns 0 on success and returns -1 on error

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chown () …Contd….

Example :

ret = chown(“test.c”,0,1);

if ( ret == -1 ){

printf(“error in changing the owner and group of the file”);

}Changes the owner and group of the file test.c as root and others respectively

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lseek ()

* lseek() changes the position of read-write pointer for the file descriptor

int lseek(filedes, offset, origin);int filedes, origin;long offset;

lseek() returns new-value of the pointer on successreturns -1 on error

The value of the pointer depends on origin :0 set the pointer to offset bytes from the begining of the file1 increment the current value of the pointer by offset2 set the pointer to the size of the file plus offset bytes

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lseek () …Contd...

Example :

ret = lseek(fd,1000,0);

if ( ret == -1 )

{

printf(“error in seeking to the 1000’th byte of the file “);

}

lseek(fd,1000,0) skips the first 1000 bytes of the file and starts reading from the 1001’th byte

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fork ()

* fork() creates a new process which is a child process

* Child process is a logical copy of the parent process

* Parent’s return value is the process id of the child

* Child’s return value is 0

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getpid () getppid () getpgrp ()

* getpid() returns the process id of the calling process

* getppid() returns the parent process id of the calling process

* getpgrp() returns the process group of the calling process

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EXAMPLE fork () , getpid () , getppid (), getpgrp ()

#include <stdio.h>main(){ int id ; int pid , pgrp ; int ppid ; id = fork(); printf (“PPID - %d PID- %d id - %d \n”, getppid() , getpid() ,id ); printf (“PGRP - %d \n “, getpgrp() );}

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EXAMPLE fork () , getpid () , getppid (), getpgrp ()

Output

PPID - 371 PID - 372 id - 0 - From child ProcessPGRP - 136

PPID - 136 PID - 371 id - 372 - From Parent ProcessPGRP - 136

PID - Process-ID

PPID - Parent Process - ID

ID - Returned value from fork()

PGRP - Process-group-ID

If PID is equal to the process PGRP then the process is the group leader

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wait () & execl ()

* wait() causes a parent to stop running and await the termination of a child process

* execl() overlays the original process with a new set of instructions

Example on execl()#include <stdio.h>main(){

int id;printf ( “Parent process \n”); if ( ( id = fork() ) == 0 ){

printf(“Statement from child process\n”); execl(“/bin/date”,”date”,0);

}printf(“ Parent process again \n”);

}

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EXAMPLE ON execl()

Output

Parent ProcessStatement from child processParent process againTue Sep 10 11:34:17 1991

Process forked two processes and parent process avoided execl() to print the final statement i.e parent process did not wait for the child to finish

To make the parent wait for the child to finish - wait() can be used

The example on execl() gets modified as

#include <stdio.h>main(){

int id;printf ( “Parent process \n”); if ( ( id = fork() ) == 0 ){

printf(“Statement from child process\n”); execl(“/bin/date”,”date”,0);

}wait();printf(“ Parent process again \n”);

}

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OUTPUT OF THE MODIFIED EXAMPLE

Parent Process

Statement from child process

waits for the

child to finish

Tue Sep 10 11:34:17 1991

Parent Process again

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The UNIX Operating System

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