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Thursday, October 4, 2012

Directory Structure and basic commands to start using linux

Directory Structure In 'Linux' :
' / '  - Root Mount Point
' ~ '  - Home Directory For User
' . '  - Reference To Current Directory
' .. ' - Reference To Parent Directory Of Current Directory

Purpose Of The Above Directories:

root :
Like Administrator In Windows.

Contains Files Which Can Be Accessed From Any Where .
Eg: date , cal ....

Contains Files Like "Device Drive Files"(Eg:Device Driver For USB etc) Which Are Necessary For Applications To Run On OS.

Contains Various Files And Folders For Modification Of System Properties (Like Control Panel In Windows). Basically Accessed By 'root/admin' user. 

Contains Various Folders For Different Users On The Network.

Command/Shell Prompt In Linux:

$ -  For Regular User
# -  For Root/Admin User

[user@Host WD]$ - Is The Way We See The Terminal Prompting Us.

Eg: [user2@system5 ~]$ - Implies we are currently working in '~' (Which is The Home Folder allotted For user2) and he is working on system5 in the network.
'~'means home folder.

Basics Commands :

Imagine This Is The Directory Structure Present In A Linux System:

vi editor

ls - to list files and folders in current working directory

cd - change directory
eg : Assume We Are Currently working In 'dir1' 
1. ' cd dir2 ' --- changes the current directory to 'dir2' from 'dir1' .
2. ' cd .. ' -----changes current directory to parent directory i.e; 'user2'  in this case.

cal - Shows calender for current month.

clear - To clear screen for a good visibility .

mkdir - To Create A New Directory (make Directory) in The Current Working Directory.
eg : ' mkdir dir1 ' - creates a new directory ' dir1 ' in current working directory

cat - For Editing Files
eg : Assume Current Directory is 'user2'

1. ' cat>test.c ' -- Creates a New File Named 'test.c' in Current Directory And Prompts Us To         Enter Data Into The File.
Note : [ctrl+d] to stop entering data .

2. ' cat test.c ' -- Displays The Contents Of  test.c ,if it already exists.

3. ' cat>>test.c ' -- Opens test.c to append (or) add at the End Of File .

Note : Editing A File Using  ' cat ' Command Is not possible .

cp  - To Copy a File To Other Location/Locations.

eg : ' cp file1 file2 ' -- Copies Contents in 'file1' to 'file2'

mv - This Is Like Cut & Paste In Windows .

eg: ' mv file1 file2 ' -- copies contents of 'file1' to' file2' and deletes 'file1'.

rm - Remove An Existing File

eg : ' rm file1 ' -- deletes 'file1'

rmdir - To Remove An Empty Folder

rm -r - To delete A Directory (Recursive Deletion)

linux commands for beginners

Task :
1. Assume Our Current Working Directory Is 'dir1'

Task 1: To Copy test.c to 'dir1' directory .
Command :  cp  ../test.c  dir1
              cp  ../test.c  ./

Task 2 : Batch Removal of Directories .
Command : rm -r  dir1  dir2

Vi Editor Commands:

' vi welcome.c ' - Creates And Opens A File Named welcome.c in vi Editor For Editing.(Remember we can not edit files Using cat command,so using an editor like vi editor is mandatory to modify/edit a file).

In Vi Editor : Use 

' esc :wq '  -To Save And Exit
' esc :w '    -To Save 
' esc :q '     -To Exit with out saving

Note : press 'a' to append or modify or to take vi editor into INSERT mode.

Note : ' ctrl+d ' in Linux is like ' alt+f4 ' in Windows , which is used to close the current window/application/task .

' ctrl+d ' can also be used to logout from current user .
' poweroff ' or ' halt ' commands in terminal will directly shutdown the system .