vi foo.txt
--

 -- in and out :q!
 -- cmd mode vs insert mode
 -- cursor movement hjkl
 -- i : insert mode
 -- a : append mode
 -- :q!		no write and quit
 -- :wq!	write quit 
 -- x		cmd mode to remove one character
 -- 5x		remove 5 characters
 -- dd		delete one line
 -- 2dd		delete two lines
 -- dw		delete one word
 -- y		yank
 -- yw		yank a word
 -- 2yy		yank 2 lines
 -- p		paste
 -- $		to end
 -- 0		to front
 -- /		search then n to next
 -- u		command mode undo

 -- modify something and save
 -- esc		insert mode --> cmd mode


echo

env variable
--
echo $SHELL
echo $HOME

vi ~/.bashrc
PS1="hello-> "
:wq!
source ~/.bashrc

mouse copy paste
mouse left drag (copy)
mouse right click (paste)

mkdir		make a directory
rmdir		remove a directory, cannot remove empty dir, use rm -fr to remove a non empty dir
cd		change directory
rm		remove a file
rm -fr		force to remove whole directory
pwd		show currrent directory
cd ..		move up directory
cd ~		cd to HOME directory just like cd

change bash system prompt
source ~/.bashrc