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
3
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.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
Evolution
Development
Standard release- AT&T versions
BSD UNIX
Other implementations of UNIX
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Features of UNIX
UNIX Philosophy
UNIX operating system
UNIX Kernel
Programming Environment
Design Principles
Limitations
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Evolution

Primarily influenced by MULTICS

MULTICS
- Developed for GENERAL ELECTRIC 645
mainframe computer
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- 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
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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
•
•
Version 6
•
•
•
•
Version 7
Version 8
•
•
•
Written in C
Moved to PDP - 11/45 and
PDP - 11/70
Released in 1975
8 use by universities only
For
Released in 1978
First commercial version but
primarly used in universities
32V - VAX version
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
•
•
Released
in 1983
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Enhancement of System III
•
•
Released in 1984
Enhancements of System V , Release 1
System V
Release 3
•
Released in 1988
System V
Release 4.0
•
System V
Release 1
System V
Release 2
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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
10 Virtual memory, Demand paging
to the VAX version 32V
UNIX 4BSD
•
•
•
UNIX 4.1 BSD
•
DARPA - funded Development
Provided support for DARPA TCP/IP
C-Shell , ex/vi , new compilers for PASCAL
and LISP were added
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
IBM PC/IX
Zeus
DEC Ultrix
HP-UX
UNIX
Elxsi UNIX
Pyramid UNIX
Data General UNIX
Perkin Elmer UNIX
MassComp UNIX
NBI UNIX
Amdahl UNIX
Microsoft’s UNIX operating system
to run on microcomputers
IBM PC
Zilog Computers
DEC
11
HP
SUN
ELXSI
Pyramid
Data General
Perkin Elmer
Mass Computers
NBI
Amdahl
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UNIX Features
Multitasking
Multi-user
Performing tasks simultaneously rather than
sequentially
e.g., While printing a document , start editing
another document
Each task is considered to be a process
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
locations as far away
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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
16 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 &
Applications
Specific capabilities added on to the OS
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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
Handling
Swapping
Page
Replacement
Character
I/O System
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Block
I/O System
Demand Paging
Terminal
Drivers
Disk & Tape
Drivers
Virtual
Memory
Kernel Interface to the Hardware
Terminal
Controller
Device
Controller
Memory
Controller
Terminals
Disks & Tapes
Physical
Memory
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The UNIX Kernel
Networking
Services
File Management
And Security
Input / Output
Services
Date and Time
Services
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UNIX
SYSTEM
Signal
Handling
KERNEL
Process
Scheduling
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
*
*
*
*
*
*
*
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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
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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.
2.
3.
4.
5.
6.
7.
8.
9.
File System Layout
Concepts of file
Features of File system
Starting and Ending
a session
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File Management utilities
Directory Management
File operation
Mountable File System
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
block
Super
block
Inode
list
Data
block
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Boot block
-
generally occupies the first sector
may contain bootstrap code
-
Information about the file system
How large, where free and other details
-
Contains a list of inodes
One inode is the root inode
-
Contains file and administrative data
Allocated data can belong to that block
only
Super block
Inode list
Data 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
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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 Subdirectory)
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 )
Block file
Disk Drives (hd0,fd0)
Transmits data Character by
Character
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
*
e.g.,
A file is identified by the path name from the root
/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
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- write and
- execute
*
Removable
*
File Independence -
*
Time stamp on each file
- Modification time
- Access time
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Unix
dev
bin
lib
/
bin
console
lp0
tty0
src
sh
csh
--Libc.a
---
uch
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tmp
man
---
bin
local
lib
--usr
include
spool
etc
spell
troff
---
*.h
tmac
passwd
group
init
---
lib
troff
--tmp
---
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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
-
/usr/lib
-
Include files for language procedure
Examples : C-header files
stdio.h, math.h
Archive libraries
Example : troff
/usr/mail
-
/usr/news
-
News files
/usr/spool
-
Spool files
/usr/tmp
-
Temporary files
/usr/src
-
Program Source Files
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Mail files
Example : mailbox
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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
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Listing of
files within
Directory
Write
Allows changing
of file contents
Creating new
files within
Directory
Execute
Executing file as
a command
allowed
Searching the
Directory 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
logout
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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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File Management Utilities
Directory
Management
Operation
cd
pwd
mkdir
rmdir
mvdir
File Comp.
Security
cmp
comm
passwd
crypt
chown
chgrp
umask
chmod
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File
contents
File
compression
Mountable
file
cat
ls
wc
file
pack
unpack
mount
umount
Copy, Move
Remove & Time
cp
ln
mv
rm
touch
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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 the
41command 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
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Directory Management
cd
cd..
cd.
e.g.,
$ cd /usr/trg/c
$ cd ..
$ cd ./c
or $ cd c
$ cd
mkdir
$ mkdir pathname
Change working Directory
Parent Directory
Current Directory
( current Directory is c )
( current Directory is trg )
( current Directory is again c )
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( home directory - in this case /usr/trg)
Make a Directory
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
*
rm -r
Remove a Directory
$ rmdir pathname
Directory should be empty, or else
(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
$ cat f2 > f3
$ cat f4 >> f3
$ cat try[0-3] > final
$ cat test* > report
Takes input from file f1 & puts it
on file f2
f3 contains the contents of f1
Appends
the contents of f4 to
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file f3
The file final contains contents
of try0, try1, try2 try3
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
-s
all entries including dot files
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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-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
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-r—r—I smj proj1 3076 Mar 3 15:08 test.c
10936 - inode number of file test.c
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wc
Word Count
$wc [Options] filename
Options
e.g.,
nl
Display no. of lines, words, characters
-I
Display no. of lines
-w
Display no. of words
-c
Display no. of characters
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$ wc test.c
20 200 5678
20 - lines
200 - words
5678- characters
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
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.,
rm
$ mv old.c new.c
Renames the file old.c as new.c
Deletes the indicated file(s) files
rm
-i
-f
-r
touch
e.g.,
removes files and directories
remove interactively
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forcible remove
remove recursively
• Dangerous
• used in conjunction with -i
Updates access, modification or change times of a file
-a
update access time
-m
update modification time
-c
prevents creating the file
$ 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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File Comparison
cmp
number and
Compare two files
If files are same no output is sent to the terminal, or else The line
the byte at which the first difference occurs is reported
-s
Outputs nothing Registers return code
Return code
0
1
2
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if files are identical
if files are different
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
-b
-e
$diff [Options] file1 file2
Ignores trailing blanks
Gives a list of ed commands so as to convert
file1 into file2.
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e.g.,
$ 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
or
pcat
e.g.,
Uncompress packed file
$ unpack try.z
or
$ pcat try.z
unpacks the file try.z
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Mountable File System
mount
e.g.,
umount
Associates a directory with a device
Mounting a floppy on the root file system
Dissociates directory from the device
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e.g.,
$ mount /dev/fd096 /mnt
$ umount /mnt
Mounts the floppy on
the directory /mnt
Dissociates /mnt from
the floppy
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File Security
passwd
To change the password
chown
To change
the ownership of the file
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$ 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
op
permission
a, u, g, o
+, -, =
r,w,x
all, user, group, others
+ add, - remove, = set
r read, w write, x execute
e.g.,
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$ 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
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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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6
Basic Utilities
1.
Line Editor
Ed
2.
Visual Editor Vi
3.
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Debuggers
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
w
-
Writing to the file
q
-
Quit
63from ed
Write :
Exiting 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,
a.*c
abc,
axyc,
a$+pmc, abcdefgc
a[b2m]c
abc,
a2c,
amc
a[0-2b-d]c
adc
a0c,
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a1c,
a2c,
a[^0-2]c
a3c,
a5c,
axc, ....
ayyyc
axc,
a[xy]*c
ac,
axc,
axxc,
a\{3,\}
aaa,
aaaa -
3 or more a’s
a\{3,5\}
aaa,
aaaa,
aaaaa
between 3 & 5 a’s
a$c
abc,
acc,
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Adding and Replacing Text..
Command
Explanation
Usage
p
print current line (s)
1,3p
l
list current line(s)
(display invisible characters like tabs etc.)
2,4l
n
print line(s) with
65 number before it
1,5n
a
append text after current line
4a
insert text before current line
3i
i
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Traversing within a file
Command
Explanation
.
Pointer to current line
.=
Gives line number
n
Current line is ‘n’
+n
Move up by n lines
-n
Move down
66 by n lines
$
points to the last line
,
short for 1,$
;
short for .,$
/.../
forward search for string
of characters enclosed between
slashes
Examples
*-
Previous line
* - Current line
*$= Prints total
no. lines but
does not
changecurrent
line
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Modifying Text
Command
d
c
m
t
j
u
Explanation
delete line(s) in text
change line(s) in text
move line(s) in text
copy line(s) in text
join lines in text
undo last command
Usage
2,5d
2,4c
2,3m5
2,3t5
2,3j
Note :
The above commands can be easily remembered by associating them with the
first characters of their action.
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Substitute Commands
(n,n)s/oldstr/newstr
s/oldstr/newstr/g
s/oldstr/newstr/p
s/oldstr/newstr&/
s/oldstr/%/
-
replaces oldstr with newstr (n,n) range of lines - optional
all oldstrs' on the current line are replaced with newstr
the replacement is only effected in print but not executed
newstr is inserted at every match
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 $/
searches for pattern at end of line
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/pattern/
the pattern is searched forward
//
forward search
??
backward search
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Command Execution
Command
Explanation
(n,n)g/findstr/commandlist
Executes given commandlist for
every occurrence of findstr
(n,n)G/findstr/
Inputs one command to execute for
every occurrence of findstr
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(n,n)v/findstr/commandlist
Executes given commandlist for every
non-occurrence of findstr
(n,n)V/findstr/
Inputs one command to execute for
every non-occurrence of findstr
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Special ed Commands
Command
Explanation
f
print current filename
w
write contents of buffer into file
w file2
write contents of buffer to file 2
r
read current
70 file
r file2
read contents of file2 after current line
e file2
edit file2 —> invoke ed on file2
!shellcmd
Execute shell command by preceding with ‘!’
! ls –l gives a listing of current directory
after current line
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The ex editor
*
*
*
*
*
an improved version of ed
less terse
provides display options like numbered
71
line
allows shorthand versions of commands
clear response for error messages
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The vi - Visual Editor
The editor
*
*
*
*
*
*
Invoking
Powerful full screen editor
vi v/s ed, ex
Mostly single key stroke commands
Interface with ‘ex’
Macro facility
Ability to process text
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$ 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
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- 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 :
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^ or (zero)
$
Character oriented
h
l
j
k
beginning of line
end of line
move left
move right
move down
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 ‘(‘ & ‘)’
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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
A
i
I
o
O
esc
Delete mode :
u
nx
ndw
ndd
D
append after cursor
at end of line
insert at cursor
at beginning of line
enter in new line after current line
enter
77in before current line
to exit insert mode
undo last command
delete n- next character
deleting n next words
deleting n lines current line and n-1 below current
line are deleted.
delete till end of line
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7
Changing Text :
nr
s
S
cw
Cut & Paste :
replace char
delete current char, enter insert mode
delete line, enter insert mode
change word
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nyy
yank n line
Named Buffers : a to z ( 26 )
Unnamed Buffers : 1
p
print buffer
J
join next line to current EOL
Join :
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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
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
^f
Scroll up half a screen
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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
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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
set nu
Nullifies the effect of auto-indent
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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
:q!
quit normally
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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
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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
important features of sdb
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SDB Commands
Command
Explanation
*r <arguments>
run the program
(arguments optional )
stepping
through the instructions
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setting a break point at line number 20
*s
*20b
(Normally break points are set at function calls)
*/pattern
*<function-name> b
\*B
*d <line-no>
*D
searches for the pattern
setting the break point at the function name
gives a list of break points\
deletes the break point at the specified line no.
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
*function:variable
character strings at the specified address
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
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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 90
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CTRACE - Debugger (Contd .)
*
Invoked as
ctrace [options] < source-file > traced-file
options :
-o
-x
print the variable in octal
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
ctest.c
-
source file
traced file
Compile the traced file as
$ cc ctest.c
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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
name
91.2
7.2
1.0
0.0
cumsecs
%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
9.34
10.08
10.18
10.24
seconds #calls
9.34
0.74
0.10
0.06
20100
1
94 100
1
msec/call
_func2
acnt
_func1
_main
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CB - C Beautification
* Beautifies the C-program code
* Indents all the statements
* Improves readability
* Invoked as
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$ 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
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Shell Features
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Shell Features
Shell Features
1.
2.
3.
4.
5.
6.
7.
8.
Various kind of shells
Shell commands
Shell Startup Dot files
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Shell variables
C Shell
Test conditions
Shell programming - Bourne Shell
Shell programming - C Shell
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Various types of Shells :
1.
Bourne Shell
sh
2.
C Shell
csh
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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
||
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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 \
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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
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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
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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
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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.,
105
shellscript
arg1
$0
$1
arg2
$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
$
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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.,
*
$ {var+thing}
$
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
If var defined then thing Otherwise nothing
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Command Environment
*
Variables & associated values
109
Shell 1
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
EXINIT
terminal type
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 CShell 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 previous
Records previous commands ! is used to execute
command
Command Format :
! <event> [ <word> <modifier> ]
<event> - absolute
- relative
- name
expr
!1
<word> -
0, 1, ...n
<modifier>
absolute
range
last
All arguments
!?su?
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!-3
!c
a-e
$
*
- 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.,
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% cd /usr/trg/SRC
% ^SRC^src
% cd /usr/trg/src
% !15
% !c
Run command 15
Run previous command beginning with c
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Changing Commands
:S/pattern/replacement
e.g.,
% !cd:s/trg/trg1
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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
{
}
%cp
Attach filenames to common root
/usr/trg4/{ac,docs,test} .
%cp/usr/trg4/ac .
%cp /usr/trg4/docs .
%cp /usr/trg4/test .
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%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
% set filec
Its usage :
:
file name completion
:
Predefined
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% set variable
% unset variable
ignoreeof
% set ignoreeof
:
To ignore all eof character ^D
noclobber
% set noclobber
:
Abandons all command using output redirection
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
$ test -f file
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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
-
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
-
128
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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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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IF
Control Flows
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.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
Redirection
Pipes
Pipe fitting with tee utility
Filters
Find
Sort
Utilities that process tabular data- cut, join, csplit
Ps and Kill133
Timely Execution- nohup, at, time
User backup utilities- tar, cpio, dd , doscp
Output related commands- pr, lpr,lp
Other utilities- sleep, sync, wait, clear, tr
Introduction to Make
Lint
Lex
Yacc
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Redirection
Metacharacter
Performs
“< “
input
“> ”
output write
“>>”
output append
e.g.,
$ who
trg1
trg2
tty00
tty02
$ who > who_out
$ cat who_out
trg1
tty00
trg2
tty02
Apr 8
Apr 8
09:33
11:10
134
Apr 8
Apr 8
09:33
11:10
$ cat date_out
Fri
Apr 8
14 : 30 :
10 est
$ who >> date_out
$ cat date_out
Fri
Apr 8
trg1
tty00
trg2
tty02
14 : 30 : 10 est
Apr 8
09:33
Apr 8
11:10
$ date > date_out
1983
1983
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Pipes :
Metacharacter
Performs
“|”
e.g.,
piping
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
-i
ignore case
-n
print line with line-number
-v
print lines which do not match
139
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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
141
$ 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
cond-list
-type x
one or more directory names
-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
x can be d, f, or c
d directory
f ordinary file
c character special142
file
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
143
- ok command
like exec , but executed interactively
e.g.,
find / -atime 7 -print
-
find / -atime +7 -print
-
find / -atime -7 -print
-
will print files accessed in
exactly 7 days
will print files accessed
earlier than 7 days
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
r
tp
u
o filenameout
numeric sorting
reverse order
use p as separator
output only lines with unique keys
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’
-on.m
output mth field of nth file
n - file no.
m - field no.
-tc
use char c’ as separator
150
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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
name
group
login
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
3432
5765
5511
2
2
2
$ kill 5511
$ ps
pid
3432
5985
time
0 : 24
154 0 : 03
0 : 51
tty
time
2
2
0 : 24
0 : 03
command
-sh
ps
somecommand
command
-sh
ps
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$ stubborn-cmd &
pid
3432
6004
5995
$ kill 5995
tty
2
2
2
time
0 : 24
0 : 03
0 : 44
command
-sh
ps
stubborn-cmd
tty
2
2
2
time
155
0 : 24
0 : 03
0 : 44
command
-sh
ps
stubborn-cmd
tty
2
2
time
0 : 24
0 : 03
command
-sh
ps
$ ps
pid
3432
6004
5995
$ kill -9 5995
$ ps
pid
3432
6103
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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
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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
r
create a new tape backup tape old files are overwritten
append files to the tape
t
x
list the names of files from backup tape
extract files from the backup medium
u
update a tape, if the named files are not present or have
been modified later on
verbose ; provides informational messages, such as the
name of each file as and when it is encountered
v
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
-p
Extract files from tape 160
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
of
ibs
obs
cbs
skip
seek
count
conv
input file name
output file name
input block size (Default 512)
162
output block size(Default
512)
conversion block size
n records before copying from I/P file
write after n output records in O/P file
n records
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
e.g.,
163
$ 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
Generates 5 column output
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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
$du
waits till all background jobs are over
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
for maintaining an up-to-date
169
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
: mod1.o mod2.o mod3.o
cc -o final mod1.o mod2.o mod3.o
: mod1.c
cc -c mod1.c
171
: mod1.c
cc -c mod2.c
: 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
173
. Unused return values
. 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
% %
user subroutines
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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]+
[-*+/]
[\t ] ;
{ return (INT); }
{ return (OPR); }
{
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
%%
180
expr : INT OPR INT
{
printf(“The input expression is correct\n”);
}
| error
{
printf (“The input expression is wrong \n”);
}
%%
Invoked as
Generates
$ yacc filename
$ yacc yac.y
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
*
Post
*
News
*
Mesg
184
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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
?
q
s [file]
w [file]
d
n or +
r
m [user]
! cmd
Prompt
quit
save (defalut mbox)
write without header
delete
next message
186
previous
reply to the sender
mail to user
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
users.
Messages can be posted on a “bulletin board” for previewing by all
News
mesg
*
*
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
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
*
rcp
*
uux
*
ct
*
cu
189
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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
/usr/spool/uucppublic
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uuto
*
*
Simplified version of uucp
Sends file to /usr/spool/uucppublic
$ uuto filename(s) system!login
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$ 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
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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
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$ 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
:
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~%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
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System calls
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System Calls :
1.
Introduction
2.
File related system calls
open()
read()
write()
creat()
chmod()
chown()
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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
*
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
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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
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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);
}
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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;
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filedesc
-
File descriptor indicating which file to be read
buffer
read
-
An area of buffer storage for holding the Characters
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;
char *buffer;
int nbytes;
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filedesc -
File descriptor indicating which file to be written
buffer
file
-
The function takes from buffer and writes them to indicated
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");
}
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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;
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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
newfile “);
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}
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;
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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”);
}
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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)
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char *filename;
int owner , group ;
filename
-
owner
-
character pointer to the name of the
file
owner id
group
group id
chown() 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 )
{
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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 )
{
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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
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* 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 ;
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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 Process
PGRP - 136
PPID - 136 PID - 371 id - 372 - From Parent Process
PGRP - 136
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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>
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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 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
The example on execl() gets modified
218 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
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waits for the
child to finish
Tue Sep 10 11:34:17 1991
Parent Process again
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