Automatically insert first character of previous line

Question

In a fortran code, I have lines like

c    write(6,*) "something"
     write(6,*) "something_else"

I would like to insert the first character of the previous line when I open a new line with o in normal mode or enter in insert mode.
In the example given, if I open a new line under the 1st line, the line should open with a c and when I open new line under the 2nd, the new line should start with a whitespace. How would I do that in vim?

P.S. Kindly add appropriate tags if you find any. I could only find vimscript and vimrc which might even be not so appropriate.

Answer 1

One possible approach is to use custom function:

function! MyFunction()
  let curline = getline(line('.'))
  let char = " "
  if len(curline)
    let char = curline[0]
  endif
  let l:r = append(line('.'), char)
  let l:r = setpos('.', [0, line('.')+1, 3, 1])
endfunction

nnoremap o :call MyFunction()<CR>A
inoremap <CR> <Esc>:call MyFunction()<CR>A

Using above mapping will make it work both in normal and insert mode.

Answer 2

Try adding this to your vimrc:

nnoremap o 0ylo^OP

where ^O is the character literal for <C-o>

The first thing that happens in the mapping is that you go to the beginning of the line 0 and yank the first character yl. Then you go ahead and create a newline below the current line o. All that's left now is to paste that character, so we execute <C-o> (which allows us to execute one normal mode command while in insert mode) and we paste that register to the left of our cursor P.