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Basic linux commands

Symbols

~   represents users home directory
.   represents current directory
..  represents parent directory of current directory

File commands

touch fileName      #Creates an empty file
vi fileName         #Open an editor to write a file
mv sourceFileName destFileName  #Rename a file
cp  sourceFileName destFileName #Copy a file
rm fileName         # deletes a file

Directory commands

mdkir directoryName     #Creates a directory
cd directoryName        #Move into the respective directory
cd ..                   #Move to parent directory
mv sourceDirectory destinationDirectory #Rename/Move a directory
cp -r sourceDirectory destinationDirectory #Copy a directory
rm -r directoryName     #Deletes a directory

Printing the contents of a file

cat fileName    #Prints the contents of a file
head fileName   #Prints first 10 lines of a file. head -100 fileName prints first 100 lines
tail fileName   #Prints last 10 lines of a file. tail -100 fileName prints last 100 lines

Other commands

su -userName    #To login as a different user
pwd     #Prints the current working directory
top     #Prints the details of various processes running on a system. Press 'q' to quit.
whoami  #Prints the userName
history #Prints the history of commands executed on a shell
!!      #Shortcut to execute the previous command
!number #Executes the command having the same number in the history. E.g., !109 executes the command 109 in the history.
kill -9 pid #Kills the process whose id is -9. 

Symbolic links to files and folders

ln -s <sourceFolder> <folderToLink>
Example:
mkdir ~/linkFolder
ln -s /data/code ~/linkFolder

Note: you must create linkFolder before executing the folder.