Mao Mao Dou Dou

– open file vertically
vim -O file1 file2
– horizontally
vim -o file1 file2

– open one file in vim, then split for the second file horizontally
:new file2
or
:sp file2
– vertifically
:vsp file2

– horizontally
ctrl + wv and :e file2
– vertically
ctrl + ws and :e file2