mjhjmtu

In vim editor, I want to replace a newline character (n) with two new line characters (nn) using vim command mode.

Input file content:

This is my first line.
This is second line.

Command that I tried:

:%s/n/nn/g

it replaces the string with unwanted characters as

This is my first line.^@^@This is second line.^@^@

Then I tried the following command

:%s/n/rr/g

It is working properly. Can you explain me why it is working fine with second command?

Oddly enough, n in vim for replacement does not mean newline, but null. ASCII nul is ^@ (control@).

Historically, vi replaces ^M (controlM) as the line-ending, which is the newline. vim added an extension r (like the C language) to mean the same as ^M, but the developers chose to make n mean null when replacing text. This is inconsistent with its use in searches, which find a newline.

Further reading:

• 
  Search and replace (Vim wiki)


• vim replace character to n

Try this: %s/$/^V^M/ (where ^V is Ctrl-V and ^M is Ctrl-M - when you type ^V it will print a ^ char then backspace over it and then when you type the ^M it will appear as ^M ... the Ctrl-V is the standard tty literal next character - run the command stty -a to show your tty's special chars).

vim use n to represent a null character in memory, that how vim handle file contain null character (while vi can not).

The use of n only match end of line in the buffer, not the newline in the string when using in expression.

See :h NL-used-for-Null and :h CR-used-for-NL for more details.

Tested with Neovim (nvim) and Vim versions

NVIM v0.3.0
VIM - Vi IMproved 8.1

Remove a newline:

cell
allele
rs2981578
fgfr2

Here, n matches newlines (to insert a newline however, use r):

:'<,'>s/n/|/g

cell|allele|rs2981578|fgfr2

Add a newline:

Nope:

cell|allele|rs2981578|fgfr2

:'<,'>s/n/|/g

cell^@allele^@rs2981578^@fgfr2

^@ is a diacritic mark for LF (line feed; see
http://vimhelp.appspot.com/digraph.txt.html#digraphs-default)

Yes:

cell|allele|rs2981578|fgfr2

:'<,'>s/|/r/g

cell
allele
rs2981578
fgfr2

To address the OP's question (how to replace one n with two, nn), just add another r:

cell
allele
rs2981578
fgfr2

:'<,'>s/n/rr/g

cell

allele

rs2981578

fgfr2

... i.e. match the original newline (n), and replace it with two newlines/carriage returns (rr).