Some vi commands

R   overwrite text beginning at the cursor.

~   upper case <--> lower case

cw  type new word, escap to remove things left.

:[x,y]s/pattern/replacement/flags
    searches for pattern between lines x and y, and replaces instances of pattern with the replacement text.
    % the entire file. $ the last line of the file. blank current line.
    flags: g to replace all, c to ask for confirmation for each replacement.

if u use the :r command, you can include the contents of another file in the vi buffer. for example the command:
:r foo.txt
inserts the contents of the file foo.txt after the current line.

the :! command allows u to enter the name of a command, which is executed within vi. for example,
:!ls -F
executes the las command and displays the results on your screen.

the :r! includes the standard output of the command in the buffer. e.g.
:r!ls -F
attaches the results to the buffer.

w   moves the cursor to the beinning of the next word
b   moves it to he beginning of current word.
0   moves cursor to the beginnning of current line.
$   moves cursor to the end of current line.

ctrl-f  moves the cursor one screen forward.
ctrl-b  moves the cursor one screen backard.

G   moves cursor to the end of file
1G  moves cursor to the beginning of file.
10G moves cursor to line 10 of file.

the pattern following a / and ? is actually a regular expression.

d$  delete everything from the cursor to the end of the line.
dG  delete everything from the cursor to the end of the file.