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Linux Command Line

1- Command Structure

Command - Options - Arguments

ls -a /var/log


  • ls -> Will list the contents of the current directory

  • ls -l -> Will list the contents of the current directory with long listing option, that will list more details like owner of the document, permissions, date of last change


2- Useful keyboard shortcuts


  • Tab : Will auto compelete the directory

  • Press Tab 2 times : If there are multiple directories with the identical first letters, double tab will give you al list of suggestions. Also if you just remember the first letters of a command double tab will give you suggestions for commands to use.

  • Ctrl + A: Move the cursor to the begining of the line

  • Ctrl + E : Move the cursor to the end of the line

  • Ctrl + Left arrow: Moves the cursor one word to the left

  • Ctrl + Right arrow: Moves the cursor one word to the right

  • Ctrl + U : Remove (Crop) characters from the cursor to the start

  • Ctrl + K : Remove (Crop) characters from the cursor to the end

  • Ctrl + Y: Paste croped text

  • Ctrl + Shift + C : Copy text to the clipboard

  • Ctrl + Shift + V : Paste text from the clipboard

  • Ctrl + R : Search command history

  • Ctrl + C : Cancel command


3- Find More Info About Commands


1- Manual pages

man ls -> Will give you information about the ls command and all the options and arguments used with it.

2- Help option

ls --help -> Gives information about the command but sometimes will refer you to the manual pages for more info


4- Files, Folders and Permissions


Basics Of Dealing With Folders


  • file myfile.txt -> Determine the type of the file

  • stat myfile.txt -> Display ownership, modification information , etc ...

  • cd -> Change directory

  • pwd -> Print working directory

  • cd sample\ project -> the back slash is used to escape the special characters and make bash know that it is a part of the directory name and not a second argument

  • ls -R -> List the contents of a folder recursively, meaning that it will also list the contents of each sub-folder

  • cd .. -> The .. represents the parent directory of the current directory

  • cd - -> Will take you to the previously used directory

  • cd -> Will take you to your home directory


Create And Remove Folders


  • mkdir new_folder -> Will create a new folder inside the current work directory

  • mkdir hello_world/new_folder -> Will create a new folder inside the sub folder hello_world

  • mkdir hello_world1 hello_world2 hello_world3 -> mkdir can create multiple folders at once

  • mkdir -p hello_word/devops/project -> Will create the parent folders hello_world and devops if they are not created yet

  • rmdir hello_world -> Removes the folder hello_world , but it has to be empty to be removed


Copy, Move And Delete FIles


  • cp devops.txt devops2.txt -> Will copy the devops.txt file to a new file called devops2.txt

  • cp devops.txt project/pipeline/ -> Will copy the file devops.txt to the project/pipeline folder

  • mv devops.txt project/pipeline -> Will move the devops.txt file to the desired folder

  • mv devops.txt project/pipeline/script.txt -> Will move the devops.txt file to the desired directory and rename it to script.txt

  • mv *.txt project/pipeline -> Move every file with its name containing .txt in the end to the desired directory

  • mv project/pipeline/* . -> Move everything in the folder project/pipeline to the current working directory

  • rm devops?.txt -> If you have files called devops1.txt, devops2.txt, devops3.txt ... etc, this command will delete all the files with the name devops followed by 1 charachter .txt

  • rm -r project -> Will delete the contents of project folder recursively


Search For Files

  • find . -name "devops*"-> Search for a file or directory with devops in its name followed by any charachters

  • find . -name "*.txt" -> Will search for any file with .txt at the end of its name

  • find . -name "*d*" -> Will search for any file or directory with letter "d" in its name


5- Super User

  • sudo -> Will give you super user permissions

  • sudo -k -> Will exit super user mode

  • sudo -s -> Will make you access the root user

  • exit -> Type exit to return from the root user to your normal user


6- File Permissions


rwx-rwx-rwx

User - Group - Others

R -> Read

W -> Write

X -> Excute

Octal Values


Read Write Excute Result
r w x 7
r - x 5
r - - 4

Read = 4

Write = 2

Excute = 1


Symbolic Values


U = User

G = Group

O = Others

A = All

"+" Will add the desired permissions to the user, group, other or all

"-" Will remove the desired permissions

"=" Will remove all the permissions and add the new values


Example:

chmod 755 test.sh

chmod a-x test.sh

Note

To change ownership of a file use chown


chown root test.sh