Hi,

a. How can we replace one more spaces with a single space in vi?
b. Replace one more spaces following a full stop or a comma with two spaces.?
c. Delete all blank line?
d. Insert > and a space at the start of every line in the file?
e. Reverse the order of lines in a file?
f. In a file, how can two consecutive lines be combined into one?

thanks,
tictactoe

a. :%s/\ */ /g;
b. :%s/[,.]\ */ /g;
c. % ! grep .
d. %s/^/> /g
e. Not quite sure what you mean on this one.
f. Place cursor on top line, press J ( shift + j ) to join the lines.

I haven't tried these, but they should work. You may have to modify them slightly. You should google for "regular expressions".

or