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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Contents :

1. Introduction & History of UNIX

2. File System
3. Basic Utilities
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4. Shell Features
5. Advanced Utilities
6. Communication Features
7. System Calls

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Chapter 1

Introduction and History of

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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 5
7. UNIX Philosophy
8. UNIX operating system
9. UNIX Kernel
10. Programming Environment
11. Design Principles
12. Limitations
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Evolution

Primarily influenced by MULTICS

MULTICS
- Developed for GENERAL ELECTRIC 645
mainframe computer
- Interactive operating system
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- 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
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Development
* Originally written in assembly language for
PDP-7
* Transportability facilitated by Thompson who
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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
8 use by universities only
Version 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 TCS Confidential
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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
9 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
Added10 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 added
UNIX 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 Microsofts UNIX operating system

to run on microcomputers
IBM PC/IX IBM PC
Zeus Zilog Computers
DEC Ultrix DEC
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HP-UX HP
UNIX SUN
Elxsi UNIX ELXSI
Pyramid UNIX Pyramid
Data General UNIX Data General
Perkin Elmer UNIX Perkin Elmer
MassComp UNIX Mass Computers
NBI UNIX NBI
Amdahl UNIX Amdahl TCS Confidential

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UNIX Features

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
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simultaneously
i.e , more than one keyboard and terminal
can be connected to one computer
Highly 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
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UNIX Features

UNIX System supplied tools

Integral utilities Basic Operation of Operating

13 like Command
system
interpreter or Shell

Tools Text print formatting like nroff

and typesetting troff

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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
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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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The UNIX Philosophy

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

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The UNIX Operating System

Kernel( Heart of Unix Operating System)

Shell Interpreter
Tools and Applications
Kernel Schedules tasks
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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 TCS Confidential

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The Users
Shells and Commands
Compilers and Interpreters
System Libraries
System Call Interface to Kernel
Signal File System CPU Scheduling

Terminal Swapping Page

Handling Replacement

Character Block 17 Demand Paging

I/O System I/O System

Terminal Disk & Tape Virtual

Drivers Drivers Memory

Kernel Interface to the Hardware

Terminal Device Memory

Controller Controller Controller

Terminals Disks & Tapes Physical

Memory TCS Confidential

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The UNIX Kernel

File Management
Networking And Security
Services

Input / Output
Date and Time
Services
Services
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UNIX
SYSTEM Process
Signal
Scheduling
Handling KERNEL

System
Memory
Administration
Management
and Accounting

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The Programming Environment

* A GOOD operating system !!

Simple yet powerful

Allows building of tools, writing of small
programs and putting them together
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A rich & productive environment

* A PORTABLE operating system !!

Written in C
Runs on a range of computers
Source code is available

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The Design Principles

* Designed for Programmers

* Interactive
* Multiple Processes can be initiated
Foreground Process
Background Process

* Methods to Co-ordinate Process20

* 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

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Drawbacks of UNIX

* Designed for computer professionals

* Not a real-time operating system

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* File Security depends on owner

* Defective programs may keep running

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Chapter 2
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File System

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The UNIX File System

1. File System Layout

2. Concepts of file
3. Features of File system
4. Starting and Ending
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5. File Management utilities
6. Directory Management
7. File operation
8. Mountable File System
9. File security

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File Systems in UNIX
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 Data

block block list block
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Boot block
- generally occupies the first sector
- may contain bootstrap code
Super block
- Information about the file system
How large, where free and other details
Inode 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
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Classification of files in UNIX

- Ordinary Files

- Directory Files

- Special Files25

- Standard Files

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Concept of Ordinary Files
* 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
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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 TCS Confidential

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Concept of Directory Files
* 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
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- 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

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Concept of Special Files

* 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

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* Types :
Character file Terminal (tty0, tty1 ) Transmits data Character by
Character
Block 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 device

Minor No.s : Different instances of the device
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Concept of Standard Files

* 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 is29called 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

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File Names

* A means for the system to identify a file

Note : Unix is case sensitive
* User accesses a file by a user-assigned file
name
* Can be a sequence of characters (a
maximum of 1430)
* 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
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Path Names
Absolute Path name

* A file is identified by the path name from the root

e.g.,
/usr/trg/c/test.c
where
test.c is an ordinary file
usr, trg, c are directories
trg is a sub-directory under usr
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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
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Features
* Hierarchical

* Security on each file

- Owner
- Group
- All others

* Separate security for

- read 32
- write and
- execute

* Removable

* File Independence -

* Time stamp on each file

- Modification time
- Access time TCS Confidential

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Unix spell
console bin troff
lp0 ---
dev
tty0 src
man
sh uch
bin csh ---
bin
--- local
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Libc.a
lib ---
---
/ usr include *.h
spool tmac
passwd lib troff
etc group ---
init tmp
---
tmp
--- TCS Confidential

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Standard File Hierarchy

/bin Basic Unix utilities cp, mv, ln

/dev Special I/O device files fd0, lp0

/etc Administrative Programs passwd, shutdown

/lib 34Unix
Libraries used by libc.a

/usr/bin Unix utilities cal, bc,spell

/usr/adm Administrative commands

and files adduser

/tmp Temporary files created

on error conditions
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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 - 35 Mail files

Example : mailbox

/usr/news - News files

/usr/spool - Spool files

/usr/tmp - Temporary files

/usr/src - Program Source Files

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Security and Access Methods

* Three levels of access

User/Owner, group, others
* Three types of access on Files and Directories
Read, Write, Execute

Access Mode Ordinary Directory

Read Examination of Listing of

File Contents 36 files within
Directory

Write Allows changing Creating new

of file contents files within
Directory

Execute Executing file as Searching the

a command Directory allowed
allowed

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Starting and Ending a Session

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
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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
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Starting And Ending A Session Contd.
passwd Change the password for the user
e.g., $ passwd

Prompt you for old password and new password

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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 TCS Confidential

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File Management Utilities

Directory Operation File Comp. Security

Management

cd cmp passwd
pwd comm crypt
mkdir chown
rmdir chgrp
mvdir 39 umask
chmod

File File Mountable Copy, Move

contents compression file Remove & Time

cat pack mount cp

ls unpack umount ln
wc mv
file rm
touch TCS Confidential

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mkdir creates a new directory

rm removes a file

rmdir removes a directory

du displays40
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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Command Structure

General Structure:
Command Name [Options] [Arguments]

E.g.,

Command Name
Tells the shell what to do
(in this case list files)
Options
Control how the41command will work
(in this case ask for a long listing)
Arguments
on which the command works
(in this case the directory
usr/trg )

ls -l /usr/trg TCS Confidential

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Directory Management

cd Change working Directory

cd.. Parent Directory
cd. 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 42
$ 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 else

rm -r (recursively remove)
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e.g.,
$ rmdir /usr/trg2 (removes directory trg2)

pwd Print Working Directory

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File Contents

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
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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

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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
45 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
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-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.c
symtab.o
treegen
test

$ Is -I -rw-rr 1 smj proj1 30766 Mar 3 15:08 symtab.c

-rw-rr 1 smj proj1 8759 Mar 3 15:12 symtab.o
47 Mar 3 15:23 treegen
-rwxr-xr-x 4 smj proj1 40743
drwxrwxr-x 1 smj proj1 53 Mar 1 09:15 test

$ Is -a .
..
.profile
.cshrc
symtab.c
...

$ Is -iI 10936-rw-rrI smj proj1 3076 Mar 3 15:08 test.c

10936 - 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
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e.g., $ wc test.c
20 200 5678
20 - lines
200 - words
5678- characters

nl no. of lines in the file and temply lists out the file
Similar to wc -l < filename >
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file Determine file types
$file [Options] [Arguments]

Options -f filelist
Normal File Types
- C49program text
- assembler program text
- commands text
- ASCII text
- English text

e.g., $ file test.c

C Program test

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cp copy a file

-i - user interactive mode

e.g.,
$ cp test.c test.c.bak
test.c and test.c.bak contain the same contents
Extra disk storage
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In Create link

e.g.,

$ ln first.c second.c
The file is referenced by two different names
No Extra disk storage

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mv Moves or renames files and directories

-i interactive mode
e.g.,
$ mv old.c new.c
Renames 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
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-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 TCS Confidential

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File Comparison

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
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0 if files are identical
1 if files are different
2 on error

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

outputs 1 indicating that the files are different

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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., 53
$ diff test1 test2

Outputs: n1 a n3,n4
n1,n2 d n3
n1,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
54 lines common to the two files
comm -23 - prints only lines in the first file but not in the
second
comm -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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File Compression

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 %
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unpack Uncompress packed file
or
pcat

e.g., $ unpack try.z

or
$ pcat try.z

unpacks the file try.z

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Mountable File System

mount Associates a directory with a device

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

umount Dissociates directory from the device

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e.g.,
$ mount /dev/fd096 /mnt Mounts the floppy on
the directory /mnt
$ umount /mnt Dissociates /mnt from
the floppy

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File Security

passwd To change the password

chown To change
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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
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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., 58
$ 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
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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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File Operation

tail Displays the last lines of file

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

head Displays the top lines of file

e.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 60
Splits the file test.c in blocks of 20 lines and creates files xaa, xab, xac

and so on, such that

xaa has first 20 lines of test.c
xab 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 horizontally

e.g., $ paste xaa xab
File xaa and xab are joined horizontally and output to the terminal
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Chapter 3
61

BASIC UTILITIES

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Basic Utilities

1. Line Editor Ed

2. Visual Editor Vi

3. Debuggers
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4. Profiling Tools

5. C-Beautification

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The Line Editor - ed

Invoking ed: $ ed filename

Prompt :
Ed has no formal prompt
P - 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
63from ed
Example :
$ ed test.c
? test.c
P
*a
<>
<>
<>
*w
*q
The edit buffer can be written to some other file also as *w filename

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Pattern Matching

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,
64 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 as
a\{3,5\} aaa, aaaa, aaaaa
between 3 & 5 as

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Adding and Replacing Text..

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

65 number before it 1,5n

a append text after current line 4a

i insert text before current line 3i

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Traversing within a file

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
66 by n lines
*$= Prints total
no. lines but
$ points to the last line does not
changecurrent
, short for 1,$
line
; short for .,$

/.../ forward search for string

of characters enclosed between
slashes

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Modifying Text

Command Explanation Usage

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 2,3j
u undo last command

Note : The above commands can be easily remembered by associating them with the
first characters of their action. 67
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 match
s/oldstr/%/ - matched strings are replaced by the replacement string in
the most recent substitute command

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Finding Text

/^ pattern/ searches for patterns at

beginning of line

/pattern $/ searches for pattern at end of line

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/pattern/ the pattern is searched forward

// forward search

?? backward search

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Command Execution

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
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(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

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Special ed Commands

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
70 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

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The ex editor

* an improved version of ed
* less terse
* provides display options like numbered
71
line
* allows shorthand versions of commands
* clear response for error messages

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The vi - Visual Editor

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
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Invoking $ vi filename
e.g., $ vi pgm.c

Modes :
* Command mode
* Insert mode
* From Insert mode Pressing
<ESC> remitts Command mode

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Types of commands
* vi-commands (invisible)

Command mode

Commands can be categorised as :

* Cursor movement
* Text manipulations
73
- 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 command
Use u to undo last command

Cursor Movement
Line Oriented :
74
^ or (zero) beginning of line
$ end of line

Character oriented
h move left
l move right
j move down
k 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 75to beginning of previous word

move

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 parenthesis
Rightly used in C- Programming for matching ( & )
76
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 cursor
A at end of line
i insert at cursor
I at beginning of line
o enter in new line after current line
O 77in before current line
enter
esc to exit insert mode

Delete mode :
u undo last command
nx delete n- next character
ndw deleting n next words
ndd 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 char
s delete current char, enter insert mode
S delete line, enter insert mode
cw change word

Cut & Paste :

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nyy yank n line
Named 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 to79
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

80
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

81
^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 :

82
/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

83
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
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: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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Debuggers :

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
85
kdb Kernel Debugger
Resides in kernel,
Allows memory examination
Disassembles instructions
Executes programs

sdb - Debugging source code written in C, Fortran 77

- Available on System V

Role The functionality of any debugger is essentially the same

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Debugger - sdb

* Invoked as

sdb <executable file>

e.g., $ cc -g test.c
$ sdb a.out 86

* 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

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SDB Commands

Command Explanation

*r <arguments> run the program

(arguments optional )
*s 87
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
88
*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
89
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
Programmers 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 90

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CTRACE - Debugger (Contd .)
* Invoked as
ctrace [options] < source-file > traced-file
options :
-o print the variable in octal
-x 91 in hex
print the variable

-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 file
ctest.c - traced file
Compile the traced file as
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$ 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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PROFILING TOOLS :

PROF and GPROF

* Improves efficiency and debugging

* gprof is available in BSD versions

* The program should have

93 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
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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
name
91.2 9.34 9.34 20100 _func2
7.2 10.08 0.74 1 acnt
1.0 10.18 0.10 94 100 _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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CB - C Beautification

* Beautifies the C-program code

* Indents all the statements

* Improves readability

* Invoked as
95
$ cb < source-file > target-file

e.g.,

$ cb < test.c > test1.c

test.c - source file

test1.c - Beautified version of test.c

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Chapter 4
96

Shell Features

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Shell Features

Shell Features

1. Various kind of shells

2. Shell commands
3. Shell Startup Dot files
97
4. Shell variables
5. C Shell
6. Test conditions
7. Shell programming - Bourne Shell
8. Shell programming - C Shell

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Various types of Shells :

1. Bourne Shell sh

2. C Shell csh
98
3. Korn Shell ksh

4. Restricted Shell rsh

5. Visual Shell vsh

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Shell Commands

Simple commands using shell Metacharacters

Exit status - return value 0 - Successful

- return value > 0 - Failure

Redirection Default input from Keyboard

Default output on the Screen
< - Read from a file
> - 99
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 the
stdin, stdout and stderr files

Pipeline sequence of commands separated by |

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; sequential execution

& asynchronous execution

&& following list executed if preceding pipeline returns

zero value
100
|| 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 \

101
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

102
* 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
103
* 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 104
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.,
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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
$ 106
varx=goodbye
$ echo $var
hello
$ echo $varx
goodbye
$ echo ${var}x
hellox

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* $ {var?message} If defined , $var
Otherwise print message
if message not defined print
default message
e.g.,
$ echo ${var?}
hello

$ 107
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?}
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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

Shell 1
109
Shell 2

Export A
e.g.,
export A

* Export from parent to child shell

* Vice-versa not true

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Predefined Special Parameters

$# number of positional parameters

$? exit value110
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 111
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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The C Shell

* Developed by Bill Joy ( Berkeley University)

* More helpful 112

interaction

* Permits shorthand repetition

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

e.g., (on - C shell)

113
% 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 114
!?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

115
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.,
116
% !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

!* All117
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\!$

118
% 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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Filename Grouping

{ } Attach filenames to common root

%cp /usr/trg4/{ac,docs,test} .
%cp/usr/trg4/ac .
%cp /usr/trg4/docs .
%cp /usr/trg4/test .
119

%ls {/usr/bin,/bin}/{ls,more}
/usr/bin/ls : not found
/bin/ls
/usr/bin/more
/bin/more : not found
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Using C - Shell
e.g.,
% cc test.c
% vi test.c
% !c
% a.out
% !v 120
% !c - o test
% test
% car /usr/trg2/document/report

% !! : s/car/cat
or
% ^car ^cat

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Variables in .cshrc of C SHELL

% set variable=value

histchars :
% set histchars=";,"
will thereafter use
; as execution character
121 character
, as substitution
history :
% 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 variable122
% 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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Test Conditions

TESTing Strings

test - z $string String length equal to zero

test - n $string String length not equal to zero

123
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

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To algebraically compare variable values

test $num1 -eq $num2

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

File related
124
$ 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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Shell Programming
- The Bourne Shell

Control flows

if command
then
commands
[ elif commands ] ...
[ else commands ]
125
fi

case word in,

pattern) commands ;;
pattern) commands ;;
...
esac

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for name [ in word ...]
do
commands
done

while command
do
126
commands
done

until command
do
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 127

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 128

- 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 resply

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Example
echo If you have a TTY vt100 enter vt100
echo If you have a TTY AT386-M enter AT386-M
echo If you have a TTY sma84 enter sma84
read term
case $term in
vt1001) TERM=vt100
;;
AT386-M) TERM=AT386-M
;;
129
sma84) TERM=sma84
;;
*) echo Invalid TERM
;;
esac
# Making it is an environment variable
export TERM
echo end of program
This can be a part of your .profile

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Control Flows
IF if (expr) then
command;
[ else if ]
command;
[ else ]
command;
endif
SWITCHswitch (string) 130
case string1:
command;
breaksw
case string2:
command;
breaksw
default :
command;
breaksw
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FOREACH foreach name (word)
commands
end

WHILE while ( expr )

131
commands
end

UNTIL until ( expr )

commands
end
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Chapter 5
132

Advanced Utilities

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Advanced Utilities

1. Redirection
2. Pipes
3. Pipe fitting with tee utility
4. Filters
5. Find
6. Sort
7. Utilities that process tabular data- cut, join, csplit
8. Ps and Kill133
9. 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 Make
14. Lint
15. Lex
16. Yacc

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Redirection
Metacharacter Performs

< input
> output write

>> output append

e.g.,
$ who
trg1 tty00 Apr 8 09:33
trg2 tty02 Apr 8 11:10
$ who > who_out 134
$ cat who_out
trg1 tty00 Apr 8 09:33
trg2 tty02 Apr 8 11:10
$ date > date_out
$ cat date_out
Fri Apr 8 14 : 30 : 10 est 1983
$ who >> date_out
$ cat date_out
Fri Apr 8 14 : 30 : 10 est 1983
trg1 tty00 Apr 8 09:33
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Pipes :

Metacharacter Performs
| piping

e.g., 135
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
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A UNIX Pipeline

Standard Input

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

136

>Prgm #5 Prgm #6

Standard Output<
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The TEE Utility :

Helps in creating the intermediate file during the pipe

operation

e.g.,
137
$ ls *.c | tee Cflst | sort
$ cat cflst

* Creates the intermediate file Cflst

* Cflst contains the list of c files

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FILTERS :

grep get regular expressions only

138
fgrep fast, several simple strings at one time

egrep extended grep, can handle more powerful

expressions like | - or operators

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$ grep pattern filenames

Options :

-c number of lines matched

139
-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
140 func1 ignoring the case
pattern

$ 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

141 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 names

cond-list
-type x x can be d, f, or c
d directory
f ordinary file
c character special142
file

-user name for a specificed user name

-group name for a specified group name
-size n File size n. blocks
If 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
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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

143
- ok command like exec , but executed interactively

e.g.,
find / -atime 7 -print - will print files accessed in
exactly 7 days
find / -atime +7 -print - will print files accessed
earlier than 7 days
find / -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 +30 144
-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 only145
check if input file is already sorted
d dictionary order letters, digits, blanks
f ignore case
i ignore non-printable characters
n numeric sorting
r reverse order
tp use p as separator
u output only lines with unique keys
o 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

146

$ 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 the147

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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Processing Tabular Data
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 or148

fields from a file
which can be of type

- Fixed length fields or

- Delimited by some character

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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....}

149
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

150
-on.m output mth field of nth file
n - 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

- 151 parameters
outputs the following

login group login

name 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 prints152

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
153
$ cat cobol 0[0-3] > file

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

* Breaks file prog.c containing C routine

upto 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 -sh
5765 2 154 0 : 03 ps
5511 2 0 : 51 somecommand

$ kill 5511
$ ps
pid tty time command

3432 2 0 : 24 -sh
5985 2 0 : 03 ps

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$ stubborn-cmd &

pid tty time command

3432 2 0 : 24 -sh
6004 2 0 : 03 ps
5995 2 0 : 44 stubborn-cmd
$ kill 5995

$ ps
pid tty time
155 command
3432 2 0 : 24 -sh
6004 2 0 : 03 ps
5995 2 0 : 44 stubborn-cmd
$ kill -9 5995

$ ps
pid tty time command
3432 2 0 : 24 -sh
6103 2 0 : 03 ps

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Timely Execution :

time Time a command

$ time wc test.c > wc.test

real 2.0
user 0.4
sys 0.3
156
nohup Protecting a process from hanging and quit signals
or interrupts

The standard output is sent to nohup.out

e.g.,
$ nohup du / &
820
Sending output to nohup.out
$ logout
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nice * Executes at specified priority
* Default priority is 24

$ nice +n Raise priority

$ nice -n Lower priority

$ nice n set157
priority

at Executes process at specified time

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

$
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User Backup Utilities :

tar tape archiver

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

tar [options] devicename filelist

Options : 158

c create a new tape backup tape old files are overwritten

r append files to the tape
t list the names of files from backup tape
x 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
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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
159
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 160
-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

161
$ 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 name

of output file name
ibs input block size (Default 512)
obs 162
output block size(Default 512)
cbs conversion block size
skip n records before copying from I/P file
seek write after n output records in O/P file
count 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
or
Copy a DOS file in UNIX format

doscp source file target file

163
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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Output Related Commands :

pr prepares a file for printing

Options
-k K col. Output
+k from page k
-lk set length of page to k lines
-p 164 page
pause after each
-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
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pr (contd.)

$ pr myfile
prepare myfile
nov 24 : 11 : 31165
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

166
$ 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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Other Utilities

sleep Suspend execution

$ sleep 5 prompt appears after 5 seconds

$ sync * updates super block

* writes all 167
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
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df displays no. of free blocks
df [option] file system

clear clears the screen and the prompt goes to

top of screen
tr replaces specified characters with other
characters 168
e.g.,
$ tr [a-z] [A-Z] < lfile > ufile
Replaces all small case letters to upper case letters

$ tr -d < tstfl > tstfl2

Deletes all the blank characters

$ tr -s \012 < try > try2

Removes adjacent blank lines in file try
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make - An Introduction

Making & Maintaining large programs

What is make? Program for maintaining large number of programs

Need for make * Difficulties in remembering the dependencies

* Simple mechanism
169 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
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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
- 170
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.c
cc -c mod1.c
171
mod2.o : mod1.c
cc -c mod2.c
mod3.o : mod3.c
cc -c mod3.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.c
INCLUDES = lim.h com.h
OBJECTIF = qp.o qex.o libs.a

query : $(OBJECTIF)
172
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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Lint - C Program Checker

* 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 173
. Unused external variables
. Unintialized variables
. Type checking features
. Portability considerations
. Statement not reached
. Excludes goto statements
* Invoked as
lint [options] filename
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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]; 174
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

175
Function argument (number) type inconsistency
scanf (arg2) int :: format int * : test.c

Value type declared inconsistently

sqrt llib-lm : test.c

Function argument ( number ) used inconsistently

sqrt ( arg1 ) : test.c

Function called with variable number of arguments

add : test.c

Function returns value which is always ignored

printf scanf
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Lex

source * General tool for separating character strings

patterns in an input

* String patterns can be specified using rules

176
syntax definitions

% %

rules

% %

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Lex Contd...

Example (on rule)

Expression > integer * integer
Expression > integer + integer
Expression > integer - integer
Expression > integer / integer
177
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

178available

Invoked as

$ lex filename
$ lex lex.l

Generates

lex.yy.c
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Yacc :

What is it? Yet Another Compiler Compiler

Features * General tool describing input to a program

179
* Specify input structure

* Code for each structure

* Outputs a subroutine which handles the input

* User supplied routine to supply next basic item

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Yacc Contd...

Specifications Declarations

%%
rules
%%
Example

%token INT OPR

%start expr
%%
expr : INT OPR INT 180
{
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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A Program using both lex & yacc

Consider this program...

#include <stdio.h>
main()
{
yyparse();
} 181

#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
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Chapter 6
182

Communication Features

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Communication Features

1. User communication commands

mail
write
talk
post
news
mesg
2. Networking commands 183
uucp
uuto
rlogin
telnet
ftp
rcp
uux
ct
cu

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User Communication Commands :

* Mail

* Write

* Talk 184

* Post

* News

* Mesg
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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>
185 user is trg)
Example : (Assume the current

$ mail trg1

Sending mail on remote system

$ mail recipient@remote_system.domain_info

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Receiving mail
$ mail Shows the message received
? Prompt
q quit
s [file] save (defalut mbox)
w [file] write without header
d delete
n or + next message
- previous 186
r reply to the sender
m [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.

187
$ 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

188
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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Networking Commands

* uucp
* uuto
* telnet
* rlogin
* ftp 189

* rcp
* uux
* ct
* cu

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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

190
-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
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uuto * Simplified version of uucp
* Sends file to /usr/spool/uucppublic

$ uuto filename(s) system!login

191
$ 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
192
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
193a specified computer
stdout to a file on

$ 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

194
$ 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
195:
~%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 7
196

System calls

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System Calls :

1. Introduction

2. File related system calls

open()
read()
write()
creat()
chmod()
chown() 197
lseek()

3. Process related system calls

fork()
getpid(), getppid(), getpgrp()
wait()
execl()

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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
198
* 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
199
- 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 mode

0 for read
1 for write 200
2 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);
} TCS Confidential

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read ()
* File should be opened in read mode

* read() an opened file

int read (filedesc,buffer,nbytes)

int filedesc;
char *buffer;
int nbytes; 201

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 reading202
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; 203

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");

} 204
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;
205

filename - character pointer to the name of the file

mode - Integer signifying the mode

The 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
206 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
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chmod ()
* chmod() set permissions for the file

int chmod (filename, mode)

char *filename;
int mode;
207
filename - character pointer to the name of the file

mode - Integer signifying the mode

The 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);

} 208
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

209 ,group)
char *filename;
int owner , group ;

filename - character pointer to the name of the

file
owner - owner id

group - group id
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chown () Contd.
Example :

ret = chown(test.c,0,1);

if ( ret == -1 ) 210
{

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;

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

The value of the pointer depends on origin :

0 set the pointer to offset bytes from the begining of the file
1 increment the current value of the pointer by offset
2 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 )

{ 212

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

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

* Parents return value is the process id of the child

* Childs return value is 0 213

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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

214

* 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 ; 215
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 Process

PGRP - 136

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

PGRP - 136
216
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() 217
{
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 Process
Statement from child process
Parent process again
Tue 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
218 as
The example on execl() gets modified
#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);
} TCS Confidential

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OUTPUT OF THE MODIFIED EXAMPLE

Parent Process

Statement from child process

219 waits for the
child to finish

Tue Sep 10 11:34:17 1991

Parent Process again

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