Important Shortcuts:

• Open Terminal or Press: Ctrl + Alt + T
• Lock the Terminal: Ctrl + S
• Unlock the terminal: Ctrl + Q

Linux Commands:

1. pwd : Present working Directory
2. exit : exit from terminal
3. cd <Directory_name> : Changes the directory
   1. cd ..  : bring the user above one directory
   2. cd / : Navigates to the root directory
   3. cd /home/user/Desktop : Navigates directly to Desktop
4. ls : List files
   1. ls <directory_name> : List content of a particular directory
   2. ls / : content of root directory
   3. ls -l : : It will show the list in a long list format
   4. ls -a : : Enlist the whole list of the current directory including the hidden files
5. date : Displays current date
6. cal : Display Calender of current month
   1. cal <month> : (eg cal aug) Display calender of the given month
   2. cal <year> :(eg cal 2024)- Display the full calendar of the given year
   3. cal <month> <year> : (eg. cal aug 2024) - Display calender of the given month and year
7. pwd : Present Working Directory
8. bc : The calculator [crtl +d to exit]
9. man command : Manual for the given command
10. Shutdown
    1. shutdown : schedules a   shutdown
    2. shutdown -c : Cancels a scheduled shutdown
    3. shutdown now : Shuts down immediately
    4. shutdown -r : Reboots the system

File & Folder Operations:

1. mkdir <directory name>: creates a new directory
2. rmdir <directory name>: removes a directory
3. rm <filename>: Removes the given file
4. rm -r: removes a directory recursively
5. rm * : deletes all files in the present working directory
6. rm -r *: deletes all files and folders recursively from the present working directory
7. cp filename location: copy file to another location
8. mv filename location: Move a file to another location
9. mv filename newfilename: rename a file
10. echo Text > filename : Creates a new file and writes the text in the file
11. echo text : writes the line of text in the terminal
12. cat filename: Reads the content from a file and displays on the terminal
13. wc filename: shows the line / word / character count of the given file

More File system commands:

1. lp <filename>: Prints a file and returns the job ID
2. cancel <job id>: Cancels an ongoing print job
3. df : Displays available disk space
4. gzip <filename> : Compress a file with .gz extension
5. gunzip <gz file> : Uncompress a file with .gz extension
6. tar -zcvf <new file .tar.gz> <foldername>: Zip a folder
7. tar -xvzf filename.tar.gz Unzip a tar file

Advanced File System Commands:

1. Grep <searchword> <filename>: Search a text in the given file
2. /pat: Search a pattern
3. touch <filename>: change timestamp of a file
4. chmod <permission> <filename>: Changes file permission [777]

   File Permissions:

   Read permission- 4
   Write permission- 2
   Execute permission- 1

5. chmod o+x <filename> :assigns execute permission to others

   Abbreviations for chmod

   Category	Operation	Permission
   u- User	+ Assign permission	r read permission
   g- group	- Remove Permission	w Write permission
   o- Others	= Absolute permission	x Execute
   a- All

6. chmod o+x,g-w <filename>:update multiple permissions
7. chown <username> <filename>: Change ownership of file
8. find <path> <selection criteria> <action>: Finds a file in the given path

eg: find /home -name a.txt -print

eg. find /home -name '*.txt'           [We can use wild card character]

Note: Wildcard characters are those characters that can stand for unknown characters. In linux ? is used for single character and * is used for multiple characters

Redirecting Input, Output, Error

> Performs overwriting of existing data
>> Performs appending to the existing data
Example: cat 1>output.txt

Eg. cal adadasdasd 2>error.txt

< Performs input redirection
Eg: cat 0< a.txt

Redirecting output using pipe

Command > filename: the output of the command will be printed to a file

Example:

Ls -l >a.txt

/dev/null : All outputs are by default redirected here whose size always remains zero

Piping:

Output of a command will be input of another command using pipe. We can use pipe using vertical bar sign (|)

Example: ls | wc -w

ls -l | wc -l

$ cat file2.txt | sort  | uniq

In the above commands, the output of ls command will be input of wc command

The VI Editor:

Modes: 

1. Command mode
2. Insert mode
3. Last line mode

• Command mode to Insert Mode: Press I,o,a,r,s [Press esc to back to command mode]
• Command mode to last line mode: Press : [Press enter to back to command mode]
• Create new file with VI editor: $vi filename
• Default mode is Command mode.
• Display the current mode- :set showmode
• Saving the text- :wq

Commands:

1. i :Insert text
2. a : Append text at cursor position
3. A : Append text at the end of line
4. o :Opens a new line below and enters insert mode
5. O :Opens new line above and enters insert mode
6. dd :Deletes a line
7. R :Replace more than one character
8. r :Replace one single character
9. s :Replace one single character with multiple characters
10. S : Replace the entire line irrespective of cursor position

Navigation Commands

1. h (or Backspace) : Moves cursor left
2. l (or Spacebar) : Moves cursor right
3. k :Moves cursor up
4. j : Moves cursor down
5. 5l : moves 5 characters right [Similarly can move any number of characters in all direction]
6. 0 (Zero) :Moves to beginning of a line
7. $ :Moves to end of a line

Editing Commands

1. x :Deletes character from cursor position
2. X : Deletes character to the left of cursor
3. J : Joins current line with next line
4. D :Deletes from cursor to end of line
5. yy :Yanks current line (Copy)
6. p :puts the deleted or copied text
7. P :puts the deleted or copied text before cursor position
8. u :Undo last editing instruction
9. U :Undo all changes made in the current line

Splitting window

1. :sp :Splits window and both windows contains the same file
2. :new :Splits window. The new window is not associated with any file
3. Ctrl+w :Switch between windows
4. :e :file Opens / Creates a file
5. :q :kills the current window
6. :on :Make the current window, only window of the screen

Last Line commands:

1. :w : Saves the text in file
2. :x :Saves file and quits editing mode
3. :wq :Saves file and quits editing mode
4. :q :Quits editing mode when no changes are made to file
5. :q! :Quits editing mode discarding changes
6. :w [filename] : Save a new file
7. :w >> [filename] : appends the content to another file
8. Ctrl +z :Stops current session and escapes to unix shell

System Administration

1. sudo <command> : Runs command in super user mode. Enter username and password when it prompts
2. su: Enters super user mode (Denoted by #)
3. passwd : change password of current user. You can enter a new password.
4. passwd <username> : Prompts appear for password of a specific user user
5. logout : logout from current user
6. who: Display the available users in a system
7. who am i:Displays the current user
8. uptime :Displays how long system is running
9. adduser <username> <options>:Creates a new user
10. userdel <username>:
11. apt list -installed:Displays list of installed applications / packages
12. apt-get update:Updates all the packages
13. apt install <package>:Installs a new package [Internet connection is required]
14. apt purge <package>:Deletes a Package and associated configuration files
15. apt remove <package>:Deletes only the package

Network Administration

1. ifconfig: [apt install net-tools] : Interface Configuration Displays Connectivity information of the system
2. ping <domain name or ip>: (Packet Internet Groper)Transfers data packets to check network connectivity
   eg: ping google.com
   ping 194.245.10.56
3. wget <exact file path>: Downloads a file from internet and stores in present working directory
4. hostname: Displays the hostname of your system.
5. Netstat: Network Statics. Displays all open sockets
6. dig <domain name>: Display information about a domain
7. nslookup <domain name>: Same as dig. Older version of dig
8. iwconfig: Provides wireless configuration