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LINUX ProgrammingIntroduction to LINUX
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What is LINUX?
An Operating System (OS) Mostly coded in C Machine independence It provides a number of facilities:
management of hardware resources directory and file system loading / execution / suspension of
programs
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History (Brief)
1969 First UNIX at Bell Labs The MULTICS Kernighan, Ritchie,
Thompson 1970’s
Bell Labs makes UNIX freeware
Berkeley UNIX (BSD) Bill Joy vi editor, C
Shell
1980’s System V release 4 TCP/IP Sun Microsystems
Solaris Microsoft Xenix, SCO MIT X-Windows
1990’s GNU, LINUX Stallman, Torvalds
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Why Use LINUX?
multi-tasking / multi-user lots of software networking capability graphical (with command line) easy to program portable (PCs, mainframes,
super-computers)
continued
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free! (LINUX, FreeBSD, GNU) Popular not tied to one company Wider choice active community
Next
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Your Account
Each user has their own space called their account.
Type your login ID and password to enter your account.
Only if the login ID and password match will you be let in.
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Login to your Account
login: ad You type your ID and RETURN.
Password: You type your password and RETURN. It does not appear.
$ The UNIX prompt (or similar). You can now enter commands.
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Logout from your Account
logout
or
^D Press CONTROL and D together
orexit
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On-line Help
man Manual pages Spacebar to go on; ^C to
stopman gnuchess
man man
apropos topic Lists commands related to topic
apropos game
apropos help
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Hardware
Kernel
Compilers
Inte
rne
t To
ols
Unix
Comm
ands
Databas
e Package
s
Other A
pplicatio
n/
System Softw
are
Shell
Shell
Shell
Shel
lUser
Use
r Use r
User
Kernel-Shell Relationship
Next
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The Shell
The UNIX user interface is called the shell. The shell does 4 jobs repeatedly:
displayprompt
executecommand
processcommand
readcommand the shell
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Typing Commands
Try these:date
cal 3 2005
who
ls -a
man cal
clear
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Changing your Password
The command is:passwd
It will ask you for the new password twice.
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Date Commands
date Gives time and date
cal Calendarcal 1997
cal 3
cal 7 1962
cal 9 1752
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You and the System
uptime Machine’s ‘up’ time hostname Name of the machine
whoami Your name who
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Calculators
expr e Simple arithmeticexpr 3 + 5 + 7
bc Programmable Calculator
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Some General Purpose CommandsSome General Purpose Commands
date date locatelocatecal cal moremorewhowho passwdpasswdls ls echoechomanman bannerbannerclearclear tty tty uptimeuptime uname uname
hostnamehostname tput tput
quotaquota spell spell
whoamiwhoami ispell ispell aproposapropos catcatwhatiswhatis sortsortwhichwhich pwdpwd
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Redirection, pipes , processes Output can be redirected to a file with‘>‘:
ls > dir.txtcal 2004 > year2004
Output can be appended to a file with ‘>>‘cal 2004 > yearscal 2005 >> years
Pipes : sending the output of one program to the input of the otherls | sort
who | sort
Processes : Running two commands sequentially
locate mj > xxx; date
locate usr > xxx &
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The UNIX File System
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The File
Ordinary Files
Directory Files
Device Files
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Ordinary files Ordinary files can contain text, data, or program
information. Files cannot contain other files or directories. Unlike other operating systems, UNIX filenames are not
broken into a name part and an extension part (although extensions are still frequently used as a means to classify files).
Instead they can contain any keyboard character except for '/' and be up to 256 characters long (note however that characters such as *,?,# and & have special meaning in most shells and should not therefore be used in filenames). Putting spaces in filenames also makes them difficult to manipulate - rather use the underscore '_'.
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Directory Files Directories are containers or folders that hold files,
and other directories.
Device Files To provide applications with easy access to
hardware devices, UNIX allows them to be used in much the same way as ordinary files.
There are two types of devices in UNIX - block-oriented devices which transfer data in blocks (e.g. hard disks) and character-oriented devices that transfer data on a byte-by-byte basis (e.g. modems and dumb terminals).
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The Parent Child Relationship
A simplified UNIX directory/file system:
/
etc bin usr1
faculty
dev tmp
date cal. . .. . . . . .. . .
mj
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System Directories / root directory /home Home directory for all users /bin and /usr/bin all commands /sbin and /usr/sbin admin commands /etc configuration & system data files (e.g. /etc/passwd) /dev files representing I/O devices (they don’t occupy
space on disk) /lib and /usr/lib Library files in binary form. /usr/include Standard Header files used by C
Program /tmp allows users to create temporary files. /var Variable part of file system
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Pathnames
A pathname is a sequence of directory names (separated by /’s) which identifies the location of a directory.
There are two sorts of pathnames absolute pathnames relative pathname
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Absolute Pathnames
The sequence of directory names between the top of the tree (the root) and the directory of interest.
For example:/bin/etc/terminfo/export/user/home/ad/export/user/home/s3910120/proj1
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Relative Pathnames
The sequence of directory names below the directory where you are now to the directory of interest.
If you are interested in the directory proj1:proj1 if you are in s3910120s3910120/proj1 if you are in homehome/s3910120/proj1 if you are in user
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Commands and Pathnames
Commands often use pathnames.
For example:/usr/games/fortune
cat /etc/passwd List the password file
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pwd Print name of current working directory
Move back to directory (the parent directory):cd ..
When in proj1, move to proj2 with one command:cd ../proj2
../proj2 is a relative pathname
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Special Directory Names
/ The root directory . The current working directory .. The parent directory
(of your current directory)
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Examples
cd / Change to root directory cd ~ Change to home directory cd (Special case; means cd ~)
cd ../.. Go up two levels.
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Investigate the System
Use cd cat file List file
cd /etc
cat passwd
ls Directory listingls List current dir.
ls /etc List /etc
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Making / Deleting / Renaming Directories
Usually, you can only create directories (or delete or rename them) in your home directory or directories below it.
mkdir Make a directory
rmdir Delete a directory
mv Rename a directory
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Permissions
ls –l /etc/passwd-rw-r--r-- 1 root root 2365 Jul 28 16:19 /etc/passwd
read, write, execute (r w x) - rw- r-- r-- directory owner group everyone
chmod -w, +w ….
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Commands to work with files
cat > filename less head tail cp mv rm wc grep spell ispell
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ls: listing directory contents• ls -- listing order numerals, UPPERCASE, lowercase
• ls –x -- displays multicolumnar output
• ls –Fx -- in o/p * indicates executables and /refers to directories
• Ls –a -- lists (.) (dot) files
• ls –l -- output in long format
• -R -- recursive list
• -r -- sorts filenames in reverse order
• -1 -- one filename in each line
• -d dirname -- lists only dirname if dirname is a directory
• -i -- displays inode number
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Handling Ordinary files
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cat : displaying and creating files
To display the contents of the small files$ cat dept.lst -- dept.lst should be present in the current directory
• Cat also accepts more than one argument. $ cat file1 file2 The contents of file2 is shown immediately after file1.
cat concatenates the 2 files, hence its name. Options with cat (-v and –n) (not POSIX rec.)-v --- displays non printable characters-n --- displays the numbering lines. (else use pr)
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Creating files using cat
$cat > file1
> First file created using cat command.
<ctrl+d>
$_ - returns to shell prompt
$ cat >> file1 -- appends to file1
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Copying a file - cp$ cp file1 file2 $ cp file1 /data/official - file1 is copies into /data/official
$ cp file1 /data/official/letter1 - file1 is copied to /data/official as letter1
$ cp /home/mca01/p1.c p1.c -- p1 is copied as p1.c in current directory (destination is a file)
$ cp /home/mca01/p1.c . -- destination is a directory
$ cp file1 file2 file3 off_data -- copying multiple files, here the last filename must be a directory and must be an existing directory.
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cp options
$ cp –i file1 file2 -- interactive copying
$ cp –R off_data official - copies directory structure.
• Here off_data and official are directories.
• If official directory does not exists then cp creates it.
• If official directory exists then off_data becomes a subdirectory under official.
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Deleting files : rm$ rm file1 file2 -- deletes file1 and file2 in the current directory.
$ rm /data/file1 /data/chap2 -- using absolute pathnames
$ rm /data/file[12] -- similar to the previous one.
$ rm –I file1 -- interactive deletion, asks for confirmation before deletion.
$ rm –r * or rm –R * -- recursively deletes the directories and subdirectories.
$ rm –rf * --- the –f option forceably removes the files/directories
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Renaming Files : mv
mv filename1 filename2 --- moves a file (i.e. gives it a different name, or moves it into a different directory)
mv chap01 unit01 mv chap01 chap02 chap03 notes Here notes is a directory
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Security by File Permissions ls –l complete description
File Type & Permissions, Links, Ownership, Group Ownership, File Size, Last Modification Time
id for to know UID & GID chmod
Relative Permissions Absolute Permissions Option -R
chown – Change Ownership chgrp – Change Group Owner umask
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Process utilities
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Disk utilities df :- Report how much free disk space is
available for each file system separately. It shows the information like
Directory where file system is attached. Device name of the file system. Number of 512-byte blocks available. Number of files we can create. Options –t (Total), -k (Reports size in KB), -h
(Reports size in MB, GB)
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du :- Disk usage :- To find the consumption of a specific directory tree rather than entire file system. Options –s for summary of usage.
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Networking Commands
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Communicating with People
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Information on Others
users Who else is logged on?
who Information on current users
ps What are people doing?ps -au
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w What are people doing?w -sh A shorter report
Examine password info:more /etc/passwd
grep s38 /etc/passwd
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Fingering People
finger Info. on current usersfinger -l Longer information
finger user Information on user (need not be logged
in)finger ad
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finger @machine-name User info. for that machine
finger @catsix
finger @ratree.psu.ac.th
ping machine-name Is machine alive (on)?
ping catsix (^C to stop)
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Your Finger Information
chfn Change your finger entry
finger also prints the contents of the .plan and .project files in your home directory. List ‘.’ files with:ls -a
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write user Send a message to user
on this machinewrite ad
mesg n Switch off talk / write acceptance.
mesg y Switch on
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Sending E-mail
Send mail :
mail Add Subject: Shoe ProblemWhat colour are my shoes? I cannot see them at the moment because of my desk.- Jim^D
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The vi Editor
Two modes Insert i Command <ESC>
Append a Replace character r, Replace word R ….. Deleting character x, Deleting line dd Exit
Goto command mode press :wq……
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Filters
The UNIX programs that read some input, perform a simple transformation on it and write some output.
grep, egrep, fgrep tr, dd, sort Sed, awk – programmable filters
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grep
grep options pattern format filename(s)
Some option -c Counting number of occurrences -n Line numbers along with lines grep Mamata –e mamata database grep [Mm]amata database
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grep : Regular Expressions
Character sets [mM] , [aeiou] , [a-zA-Z0-9]
Immediately preceeding character G*, [gG]*
Matching a single character 2… A four character pattern starting with 2 .* A number of characters or none
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grep : RE
Specifying pattern boundaries ^r pattern beginning
with expression r
^[^r] pattern not beginning with expression r
r$ pattern ending with expression r
c Any non-special character c matches
\c Turn off any special meaning of character c
^ Beginning of line
$ End of line
. Any single character
[…] Any one of character in …; ranges like a-z are legal
[^…] Any single character not in …; ranges are legal
r* Zero or more occurrences of r
r1r2 RE r1 followed by RE r2
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egrep : Regular Expressions
r+ : one or more occurrences of r r? : zero or more occurrences of r r1|r2 : r1 or r2 (r) : nested r
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fgrep
Searches for multiple patterns Does not accept regular expression Multiple patterns are separated by new
line character.
The disadvantage of grep family is that none of them has a separate facility to identify fields.
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sort
-f : eliminates distinction between uppercase and lowercase letters.
-n : numeric comparison - r : largest to smallest +m : comparison skips first m fields +0 : beginning of the line -u : discard duplicates
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comm
File comparison command Gives three columns of the output
Lines that occur only in file 1 Lines that occur only in file 2 Lines that occur in both
One or more columns can be suppressed Comm –12 f1 f2
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tr
Transliteration of character in the input tr a-z A-N
Mostly used for character conversion
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Assignment
1. Try all the UNIX commands. Store the output in a file appropriately using redirection operators.
2. Read a word from the terminal and check if the spelling is correct. Suggest few alternatives.
3. Create a file using Vi. Store few names in the file. Search all the names containing the letter M or m.
4. Create another file using cat command5. Compare both the files to find the differences6. Use calculator commands to compute 5
arithmetic expressions.