vi ("vee-eye" is a visual editor)
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Use   % man ed
command to learn about regular expressions supported by vi editor

Some of the advanced editing features of vi editor are described below:

To set line numbers	:set nu
To remove line numbers  :set nonu

To mark a line with an alphabet label	m followed by an alphabet   e.g mx
To refer to that line use 'x	e.g.  'a,'bm'c
26 marks are maintained by vi (a thru z).

vi also maintains 26 buffers (a thru z).
To copy text and store it on a buffer use yank  e.g.  "x3yy
To cut  text and store it on a buffer use yank  e.g.  "x3dd
The command "X2yy will append the two yanked line to buffer x
The command "Xdd will append the deleted line to buffer x
The content of a buffer can be inserted at any desired location ("xp)

To change the case of the letter (upper to lower  or  lower to upper) use ~

Cursor positioning: (H - head line of the window; L - last line; M -middle line)
  On the same line: fx - move to x forward; Fx - move to x backward;
		    tx - move upto x forward; Tx - move upto x backward;
		    ; - repeat last f F t T command; , - inverse of last f F t T
  0 - beginning of line; ^ - first non white; $ - end of line;
  ctrl-g  or  :f  display the filename, current line, # of lines in work buffer

Scrolling: ctrl-f - forward full screen; ctrl-b - backward full screen
	   ctrl-u - forward half screen; ctrl-d - backward half screen
	   G - end of file; 8G - go to 8th line;

To insert special character (ESC[2J clear screen) escape character sequences 
  ctrl-v character         That character will be quoted 

To change every occurrence of a word
  :1,$s/\<word\>/newstring/g

( beginning of a sentence  and  end of a sentence )
{ beginning of a paragraph  and  end of a paragraph }
0 or ^ beginning of a line  and  end of a line $

To swap two strings on the same line
  :s/\(string1\)\(string2\)/\2\1/

  e.g.

     Here is the original three lines of text:
     Here  1 abc  2  3xxxyyyyzzz4   5   6aaabbbbccc7  8  9
     Here line  1 abc  2  3xxApplezz4   5   6aorangec7  8  9
     He  bc  2  3xxxyyyyyyyyzzz4   5   6aaaccc7  8  9
     
     The above three lines can be changed drastically
     with the following edit command
       :s/\(x.*z\)\(.*6\)\(a.*c\)/\3\2\1/
     
     as below:
     
     Here  1 abc  2  3aaabbbbccc4   5   6xxxyyyyzzz7  8  9
     Here line  1 abc  2  3aorangec4   5   6xxApplezz7  8  9
     Hmde  bc  2  3aaaccc4   5   6xxxyyyyyyyyzzz7  8  9


   The regular expression x.*z refers to the string with first occurrence of x
   followed by any character until the LAST occurrence of z.

To search a string1 not followed by string2
   /string1[^string2]/

To replicate a string on the same line
  :s/string expression/&&/
refer to man ed for the details.

For vi personal setup,
  set EXINIT variable 
  or prepare key binding & other strokes in ~/.exrc file.
  A sample .exrc file is

   set number wrapscan ignorecase showmatch sections=NHNhSH wrapmargin=0
   map [6~ 
   map [5~ 
   :map v :1,$s/^/> /

  In .exrc file, to insert any special (control) characters,
  prefix it with ctrl-v character.