Insert blank line after different lines

Question

Given file alfa.txt:

foxtrot
golf
hotel
india
juliet

I would like to insert a newline after lines 2 and 4. I have this command:

ex -sc '2pu_|4pu_|x' alfa.txt

However it is inserting lines after line 2 and 3, instead of 2 and 4:

foxtrot
golf

hotel

india
juliet

Answer 1

The commands are executed serially, which means that before the 4pu_ command is executed, a newline has already been added and your previous line 4 is now line 5.

There are at least three ways to solve this:

1. Start from the back. This way, previous changes do not affect later changes.

2. As suggested by Christian Brabrandt, you can add newlines based on a global command:

   :g/\v^%2l|%4l/pu _
   

   To understand this command, read about :h :global. Note: To save a keypress I've used \v. With \v, we don't need to escape the %l and |.

3. Manually add to the number(s), i.e. do

   ex -sc '2pu_|5pu_|x' alfa.txt
   

Answer 2

Here is an example based on the comment:

ex -sc 'g/\v%2l|%4l/pu_' -cx alfa.txt

Here is a working alternative to my original command:

ex -sc '4pu_|2pu_|x' alfa.txt