usage of vi

1. ZZ(command mode) : save and exit;
2.ctrl+f/b:page down/up
3.H/M/L:to head,middle,low of document.
4./:search forward
5.?:search backward
    n means next march in searching
6.dd:delete line
7:x:delete current letter
8.p:paste to next line
9:P:paste to forwart line
10.yy:copy current line to cache
11.nyy:copy current n line to cache
12.ctrl+[=esc
13.i/a:insert before/after cursor
14.I/A:insert before/after line
15.:n:move cursor to line n