Transferred from: http://www.cnblogs.com/fortran/archive/2010/07/25/1784513.html
The command of the case conversion in Vim is: Gu or Gu, the image of a little u means to lowercase, big u means to capitalize. The next step is to define the two commands (qualifying lines, letters, words) and so on.
1. Whole article capitalization converted to lowercase
 
 
  
  When you open a file, you do not need to enter command line mode.
 
  Type: Gggug
 
 
 
 
 
  
  Explain: Gggug divided into three sections gg gu G
 
  gg= cursor to the first character of the file
 
  Gu= the selected range all lowercase
 
  g= to end of file
 
 
 
2. Whole article lowercase converted to uppercase
 
 
  
  When you open a file, you do not need to enter command line mode.
 
  Type: Gggug
 
 
 
 
 
  
  Explain: Gggug divided into three sections GG GU G
 
  gg= cursor to the first character of the file
 
  gu= all uppercase in the selected range
 
  g= to end of file
 
 
 
3. Convert only one word
 
 
  
  Guw, GUE, GUW, GUE
 
  The words that follow the cursor are then converted to uppercase and lowercase.
 
  The command to convert 5 words is as follows:
 
  gu5w, gu5e, gu5w, gu5e
 
 
 
4, convert the case of a few lines
 
 
  
  Position the cursor on the line you want to convert, type: 1gU
 
  Lowercase to uppercase conversions from the line down the cursor
 
  10gU, a 11-line lowercase to uppercase conversion
 
  And so on, there are other uppercase and lowercase conversion commands
 
  GU0: From the position of the cursor to the beginning of the line, it becomes uppercase
 
  gu$: From the cursor position to the end of the line, it becomes uppercase
 
  GUG: From the cursor position to the last character of the article, all uppercase
 
  GU1G: From the position of the cursor to the first character of the story, it becomes uppercase
 
 
 
Capitalization conversion in Vim