how to add an extra character after exactly two character on each line in vim

I have the text in the file like this:

in IDMAN
ip f开发者_如何转开发rghj

I want the text to be like this:

in *IDMAN
ip *frghj

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You can do:

:%s/\%3c/*

Explanation:

• :s is the substitute command, % is the range for all lines in the file
• / is the pattern delimiter
• \%3c is a pattern that matches nothing at third character in the line
• * is the substitution expression

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Hover your cursor over the capital I in IDMAN in normal mode.

Enter visual block selection with CTRL-V and go down a line with j.

Enter insert mode with SHIFT-I and then enter your desired character.

Go back to normal mode with ESC and the character will appear in the same column for the rest of the lines.

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For the example file:

in IDMAN
ip frghj

and the following output (a star on each line):

in *IDMAN
ip *frghj

The sequence of commands is the following (cursor has to be on the character where the addition should happen):

CTRL-vjI*ESC

That means:

• CTRL-v: Start visual block mode
• j: Mark the second line too
• I: Go into input mode for the block
• *: Insert the character(s)
• ESC: Close the visual input mode, so to all marked lines, the characters will be added.

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How to add an * character after exactly three character on each line in vim:

:%s/\(...\)/\1*/

see :help :s, :help range, :help s/\\1

or, more shortly (great thanks to @Benoit for :-) )

:%s/.../&*/

see help s/\& (thank @Benoit for being pointed to this)