Linux & shell programming

- It is a popular Multiuser and Network OS
- It was written by Linus Torwald in 1991 as a core program
for Computer's Operating System called as Kernel.
- Linux is also called as Extended version of Unix OS.
- Linux is an open source kernel that is freely available on
Internet and no licence required to use it.
- programmers can download from internet and edit it.

- There are many distributer companies of Linux they provide the different flavor of Linux :

RedHat Linux
Ubuntu Linux
Gintu Linux
Fedora Linux
Debian Linux
Linux Mint

Linux Provides GUI as well as CUI .........

CUI Environment of Linux is known as Linux shell or Terminal
The commands used in linux , are case sensitive and usually they are written in lower case(small letter).

====================================================

Characteristics / Properties / Advantages / Services of Linux :

1. Multi User

More than one user can loggin simulteneously and perform the different

task, over a single machine.

2. Multi Programming :

Linux can operate more than one program at same

time using Time Scheduling.

3.Shared Library :

Linux uses shared libray instead of making multiple copies of file . It makes the use of less disk space and memory.

4. Compatible with Old Plateforms :

It can easily install on old hardware plateform and

processors.

5. Economic :

To purchase the Linux software we have to pay

a vary nominal charge/low cost. many of the applications are freely available for linux os.

5. Samba :(Server Message Block)

This is a protocal which is used to share the files

in network and also beteen the different OS.

6. Dos Emulator

linux provides a software that executes all the dos commands

7. Apache Web Server

Linux provides the web server - apache. this make

the machine to be used as server and handle the request of client machine.

Apache is also used to develop the web Application

over the java and php

8. Multiple Distributers

As the linux is open source, so there are multiple

companies that sell the linux with some additional features. so user can go through according to their choice.

9. Development Library and gcc

Linux provide some library and inbuilt compiler -gcc

to create and excute the program in c, c++ , java etc.

10. No virus Attack

There is not virus found in Linux OS till Now. so it is

assumed as virus free OS

===========================================

Linux Architecture :

___________________________________________________

|Shell Utitilities Application Program |

|-------------------------------------------------------------------------------|

Kernel

Hardware

===========================================

Linux os is made of two elements : Shell and Kernel

Shell:

- It is the Interface provided for the User
- It manages the Commands,Instructions, Utilities and
application Software
- It provides a terminal where user can type the commands
- The command written over the shell are case sensitive
- Shell is also called as command line interpreter ,
because it translate each command to machine code
and passes to the kernel for further action

==============================================================

Linux provides different types of shell for different task like --

a) Korn shell (kcsh) : denoted by #

b) Bourn Shell(bsh) : denoted by $

c) c shell(csh) : denoted by symbol similar to 'c'

Kernel :

- It is the System program

- It is core linux code that manages,controls and operates the hardwares

- It takes the commands or instruction from shell and perform the action. the result generated by kernel is sent back to the shell

=============================================================

GUI On Linux:

- Linux provides the GUI as well CUI .

- The CUI of linux is provided by the shell

- The GUI system of linux is called as X-Windows System

- There are two types of Xwindows systems are available for linux :

1.KDE(K-Desktop Environment)
2.GNOME(GNU Object Model Environment)

===========================================

Hardware Requirement for Linux :

To install the Linux in our machine we need following Configurations:

a) Processor : x86 or higher

b) RAM : 256MB or higher

c) HardDisk : 4GB free Space

d) Keyboard

e) Mouse

f) CD-Rom (for installation)

g) Installation CD of Linux Kernel

===========================================

Directory /file Structure of Linux OS

-------------------------------------

- Linux provides an Inbuild Directory System to keep system and

user's files.

- There are many inbuilt directories in Linux OS

- Each directory is followed by / sign

/ (root)

/bin /boot /usr /etc /home /dev /lib

cat Ram (user)

cp Desktop

chmod Start

...

/bin:

- it store the linux utilities (commands) in Binary formate

- some linux command are :

cat,cp,ls,dir,mkdir,cd,date,time,.....

/boot :

- it stores the bootable files

- these files are loaded to memory when computer starts

- they are necessory to start the linux

/usr:

- it stores the files that are not used in booting process

/etc:

- it stores all the system related files.

- It also stores the user,group,account,memory related database.

/home:

- it stores the home directories of all the users

- all the user accounts are itself come in home directory

- for examle if naveen is the home directory for user NAVEEN, then it is written like :

/home/naveen

- all the files created by user NAVEEN are placed inside the home

directory of user (/naveen) like Desktop,documents,....

/dev :

- It store the information about the hardware devices like- Hard disk, pendrive,Printer, Scanner,....

- It stores the Driver related information

/lib

- It stores the inbuilt libraries

- These libraries are used for shell programming and other types of language features

=================================================================

File types in Linux :

we can catagories the files in 3 types in linux :

1. Ordinary files

2. Directory files

3. Special Files

Ordinary files:

- These are the common types of file

- These are created by users

- ex:- Data files, Program files, executable file...

- They contains the data/text/number etc.

Directory files :

- These are container of other files

- There are many of the inbuilt directory files in Linux

that holds the different types of files.

- These are followed by '/'

ex:- /bin, /boot, /home, /usr,......

Special Files :

- These are the System Files

- They can be following types :

a) Character Device Files

b) Block Device Files

c) Hard Disk Files

d) Symolic Disk Files

===========================================

Working with RedHat Linux :

1. start up and Shutdown

2. Login and Logout

3. Working with Desktop Icons

4. Setting the Desktop Environment

5. Working with Linux Shell

6. Using Linux Basic Commands

7. Creating User Account

8. Working with basic Utilities of RedHat Linux :

Text Editor

Graphics Editor

Calculator

Music Player

Web Browser

....

StartUp and ShutDown :

- when ever we start the Linux, it alway ask for username and password

- First time we have to use the System's Account to

- After starting the linux , we can also create our personal user account (user name and password) and the next time we use our personal account to Login.

- A Desktop is get displayed just similar to windows OS

that may be either KDE or GNOME

- The Desktop contains some Icons , the Start Button and task bar

- To turnoff the Linux , we use the ShutDown options

from the system or start menu

===========================================

Opening Linux Shell : (Login and Logout)

we can open multiple (atleast 6 ) terminal in Linux at

a time

to goto the terminal (or shell) we press :

ctrl+alt+f1..f6

when we open the terminal it will ask for user name and password

when you type the name and password, keep the proper case (both are case sensitive)

for security reasons , linux do not show the password

characters on screen when you type it

after successfully login, linux shows the terminal with

a sign either # or $

# denotes the root user or Administrator

$ denotes the local user (other user)

to logout from current account type the command-

- logout

- exit

to come back to desktop environment press :

ctrl+alt+f7

===========================================

RedHat Desktop Icons :

- user's Home(like-ram's Home) // My Documents

- Trash // Recycle Bin

- Computer // My Computer

An Aditional Icon will be shown when we plug the pen drive / flash drive

User's Home :

It is the Home directory of User

It is similar to the My-Document icon in Windows

It stores all the data / files created by user

Name is Like to :

Ramesh's Home : /home/Ramesh

Ram's Home : /home/Ram

Root's Home : /home/root

...

The main Directory inside the Home directory is

'Desktop'

Trash :

- This is the program that holds the deleted files

- It is similar to the windows Recycle Bin

Computer :

- It shows all the information about the hardwares

connected to system

- It also shows the local disk and other directories stored over them

- It is similar to the MyComputer in Windows OS

Linux Basic Practices :

Changing Desktop Wallpapers

Creating and removing Folders

Renaming Folders

Customzing files and folders

Creating TextFiels

Copy,Move,Cut,Paste,.....

Creating User Accounts

Working with Linux Commands :

- to run the linux command on Redhat or Ubuntu , open the

terminal (Desktop | right click | open terminal) Or (System -> Terminal)

- or you can also open the shell by pressing ctrl+alt+f1..f6

- In shell you have to again type the user name and password

- The Shell will be either willbe displayed like :-

[computerName / ] # (for root or admin)

[computerName/home/username] $ (for local user)

----------------------------------------------------------------------------

To run linux command online :

http://simpleshell.com/#

freelinuxconsole.info/terminal

tutorialspoint.com/execute_bash_online.php

----------------------------------------------------------------------------

Commands :

1. ls Command :

- this command is used to see the list of files and

directories

- only the name will be displayed

- we can use the options with ls command

- any option is followed by a single space and dash (-)

syntax:

ls [option]

options :

-a : all

-d : directories

-r : reverse

-l : long listing formate

ex:

$ ls -l

----------------------------------------------------------------------------

2. clear command :

- It is used to clear all the contents from display screen

- It is similar to cls command of the dos

syntax:

$ clear

----------------------------------------------------------------------------

3. pwd command :(Print working directory)

This command is used to display the complete path

of current working directory.

ex:

$ pwd

output: /home/gist

--------------------------------------------------------------------------------------

4. mkdir Command (Make Directory) :

This command is used to create new directory.

It is similar to md command of the DOS

Directory is created under the current directory

syntax:

mkdir Dir-name

ex:

$ ls

output:-(empty)

$ mkdir Ram

$ ls

output:-

Ram

---------------------------------------------------------------------------

5. cd command : (Change Directory)

- This command is used to change the current working directory.

we can use this command either to go inside the directory or

jump outside of directory.

syntax :

a) cd directory-Name

// to open directory

b) cd ..

// back to parent directory

c) cd /

// back to root or home directory

ex:

$ mkdir ram

$ cd ram

$ pwd

output :/home/gist/ram

$ cd ..

$ pwd

output : /home/gist

--------------------------------------------------------------------------------------

6. cat Command :

- This command is used for three purpose

i) creating a new file

ii) displaying the content of file

iii)adding new content at the end of file(appending)

i) creating new file:

cat > fileName

ex:

cat > ram.txt

......

.......

ctrl+d

ii) Displaying the contents of file :

cat FileName

ex:

cat ram.txt

...............

................

.................

iii) Appending text to file :

cat >> fileName

ex:

cat >> ram.txt

......................

...................... type some text

note:

these lines are added at the end of the file- ram

to see the new content you can use the command cat

like:

cat ram.txt

..............

.............. //old data

.................

................. // new data

7. rm command (remove) :

This command is used to remove(delete)any file.

syntax:

rm <FileName>

ex:

$ rm dca.txt

8. rmdir Command :

This command is used to remove or delete any

empty directory

syntax:

rmdir <dirName>

ex:

$ mkdir ram

$ ls

ram

$ rmdir ram

$ ls

9.cp Command : (copy command)

This command is used to create the copy of any file

Copy can be created either inside another directory

or wihin same directory

In same directory, copy is created with different name

but in another directory copy may be created with

same name

If file already exists, this command overwrite it.

Syntax:

cp <fileName> <new Name>

cp <fileName> <path>

cp <fileName> <path/fileName>

ex:

$ mkdir ram

$ mkdir mohan

$ cd ram

$ cat > dca

dca is a diploma course

it is a one year course

the minimum eligibility is 12th

Now we are going to create the copy of 'dca' with a new name

'dca1'

$ cp dca dca1

$ cat dca1

.......

//same matter as dca file

Now we are going to create the copy of dca inside 'mohan' directory

$ cp dca /home/ravi/mohan/

$ cd ..

$ cd mohan

$ ls

dca

[~/mohan]$ cat dca

.....

10. mv command(move command) :

- This command is much similar to the cp command

- It is used to move the file one directory to another

grep command in Unix/Linux

Difficulty Level : Easy
Last Updated : 15 Nov, 2022

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The grep filter searches a file for a particular pattern of characters, and displays all lines that contain that pattern. The pattern that is searched in the file is referred to as the regular expression (grep stands for global search for regular expression and print out).
Syntax:

grep [options] pattern [files]

Options Description

-c : This prints only a count of the lines that match a pattern

-h : Display the matched lines, but do not display the filenames.

-i : Ignores, case for matching

-l : Displays list of a filenames only.

-n : Display the matched lines and their line numbers.

-v : This prints out all the lines that do not matches the pattern

-e exp : Specifies expression with this option. Can use multiple times.

-f file : Takes patterns from file, one per line.

-E : Treats pattern as an extended regular expression (ERE)

-w : Match whole word

-o : Print only the matched parts of a matching line,

 with each such part on a separate output line.

-A n : Prints searched line and nlines after the result.

-B n : Prints searched line and n line before the result.

-C n : Prints searched line and n lines after before the result.

Awk is a scripting language used for manipulating data and generating reports. The awk command programming language requires no compiling and allows the user to use variables, numeric functions, string functions, and logical operators.

Awk is a utility that enables a programmer to write tiny but effective programs in the form of statements that define text patterns that are to be searched for in each line of a document and the action that is to be taken when a match is found within a line. Awk is mostly used for pattern scanning and processing. It searches one or more files to see if they contain lines that matches with the specified patterns and then perform the associated actions.

Awk is abbreviated from the names of the developers – Aho, Weinberger, and Kernighan.

WHAT CAN WE DO WITH AWK?

1. AWK Operations:
(a) Scans a file line by line
(b) Splits each input line into fields
(c) Compares input line/fields to pattern
(d) Performs action(s) on matched lines

2. Useful For:
(a) Transform data files
(b) Produce formatted reports

3. Programming Constructs:
(a) Format output lines
(b) Arithmetic and string operations
(c) Conditionals and loops

Syntax:

awk options 'selection _criteria {action }' input-file > output-file

Options:

-f program-file : Reads the AWK program source from the file

                  program-file, instead of from the

                  first command line argument.

-F fs            : Use fs for the input field separator

Sample Commands

Example:

Consider the following text file as the input file for all cases below:

$cat > employee.txt

ajay manager account 45000

sunil clerk account 25000

varun manager sales 50000

amit manager account 47000

tarun peon sales 15000

deepak clerk sales 23000

sunil peon sales 13000

satvik director purchase 80000

1. Default behavior of Awk: By default Awk prints every line of data from the specified file.

$ awk '{print}' employee.txt

Output:

ajay manager account 45000

sunil clerk account 25000

varun manager sales 50000

amit manager account 47000

tarun peon sales 15000

deepak clerk sales 23000

sunil peon sales 13000

satvik director purchase 80000

In the above example, no pattern is given. So the actions are applicable to all the lines. Action print without any argument prints the whole line by default, so it prints all the lines of the file without failure.

2. Print the lines which match the given pattern.

$ awk '/manager/ {print}' employee.txt

Output:

ajay manager account 45000

varun manager sales 50000

amit manager account 47000

In the above example, the awk command prints all the line which matches with the ‘manager’.

3. Splitting a Line Into Fields : For each record i.e line, the awk command splits the record delimited by whitespace character by default and stores it in the $n variables. If the line has 4 words, it will be stored in $1, $2, $3 and $4 respectively. Also, $0 represents the whole line.

$ awk '{print $1,$4}' employee.txt

Output:

ajay 45000

sunil 25000

varun 50000

amit 47000

tarun 15000

deepak 23000

sunil 13000

satvik 80000

In the above example, $1 and $4 represents Name and Salary fields respectively.

Touch command:-

touch command in Linux with Examples

Difficulty Level : Easy
Last Updated : 19 Feb, 2021

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The touch command is a standard command used in UNIX/Linux operating system which is used to create, change and modify timestamps of a file. Basically, there are two different commands to create a file in the Linux system which is as follows:

· cat command: It is used to create the file with content.

· touch command: It is used to create a file without any content. The file created using touch command is empty. This command can be used when the user doesn’t have data to store at the time of file creation.

Using touch Command

Initially, we are in home directory and this can be checked using the pwd command. Checking the existing files using command ls and then long listing command(ll) is used to gather more details about existing files. As you can see in the below figure there is no existing files.

Touch command Syntax to create a new file: You can create a single file at a time using touch command.

Syntax:

touch file_name

The file which is created can be viewed by ls command and to get more details about the file you can use long listing command ll or ls -l command . Here file with name ‘File1‘ is created using touch command.

Touch command to create multiple files: Touch command can be used to create the multiple numbers of files at the same time. These files would be empty while creation.

Syntax:

touch File1_name File2_name File3_name

Multiple files with name Doc1, Doc2, Doc3 are created at the same time using touch command here.

touch Command Options

Like all other command Touch command have various options. These options are very useful for various purpose.

touch -a: This command is used to change access time only. To change or update the last access or modification times of a file touch -a command is used.

Syntax:

touch -a fileName

Here touch -a command changes access time of the file named Doc1.

touch -c : This command is used to check whether a file is created or not. If not created then don’t create it. This command avoids creating files.

Syntax:

touch -c fileName

touch -c-d : This is used to update access and modification time.

Syntax:

touch -c-d fileName

touch -m : This is used to change the modification time only. It only updates last modification time.

Syntax:

touch -m fileName

touch -r : This command is used to use the timestamp of another file. Here Doc2 file is updated with the time stamp of File 1.

Syntax:

touch -r second_file_name first_file_name

touch -t : This is used to create a file using a specified time.

Syntax:

touch -t YYMMDDHHMM fileName



====================

Uniq command:

The linux uniq command is basically used to remove all repeated lines in a file. This command is used when a line is repeated multiple times and replace these multiple lines with one line. This command is designed to work on sorted files.

Purpose : Remove repetitious lines from the sorted ‘input-file’ and send unique lines to the ‘output-file’. If no ‘output-file’ is specified, the output of the command is send to standard output. if no ‘input-file’ is specified, the command takes input from standard output.

Syntax :

$ uniq [option] [input-file] [output-file]

Options :

-c : Precede each output line by the number of times it occur.
-d : Display the repeated lines.
-u : Display the lines that are not repeated.

Examples :
Create a sample input file.

$ cat sample

Input :
This is a test file for the uniq command.
It contains some repeated lines.
It contains some repeated lines.
And some are different.
It contains some repeated lines.
It contains some repeated lines.

1. Removing duplicate lines when file is not sorted.

$ uniq sample

Output :
This is a test file for the uniq command.
It contains some repeated lines.
And some are different.
It contains some repeated lines.

2. Removing duplicate files after sorting.

$ sort sample -> sample1

$ uniq sample1

Output :
And some are different.
It contains some repeated lines.
This is a test file for the uniq command.

3. Finding number of times the lines are repeated.

$ uniq -c sample1

Output :

1 And some are different.

4 It contains some repeated lines.

1 This is a test file for the uniq command.

4. Finding repeated lines.

$ uniq -d sample1

Output :

It contains some repeated lines.

5. Finding lines which are unique and store in another file.

$ uniq -u sample1 out

$ cat out

Output :

And some are different.

This is a test file for the uniq command.

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SancTutorial

grep command in Unix/Linux

touch command in Linux with Examples

Using touch Command

touch Command Options

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