Vim: diff two sections in two files, but not the entire file

vimvimdiff

I upgraded a system from Nagios 2 to Nagios 3, and now I am comparing some differences in the old and new configuration files.

There are significant changes to the configuration files, and I do not want to perform a diff on the entire file because vimdiff is showing me too many irrelevant differences and has trouble dealing with # comments at the beginning of lines, etc.

Can I use vim, or a vimdiff-like functionality to perform a diff on two particular sections in two different files?

For example, I want to diff only the lines which look something like this:

# Define a service to check the load on the local machine. 

define service{
    use                             local-service         ; Name of service template to use
    host_name                       localhost
    service_description             Blah Blah
    check_command                   Blah Blah
    }

Best Answer

It sounds like linediff.vim might be what you want: “Perform an interactive diff on two blocks of text”.

You specify each block (line range) with its :Linediff command (e.g. :4,10Linediff, or do a visual selection first, then type :Linediff (which comes out as :'<,'>LineDiff)). The ranges can be from the same file/buffer or different ones. Once you have specified two ranges, it opens a new tab that has two new, diff-mode buffers (in a split) for the specified ranges. You can edit and :w in either of these buffers to update the original ranges. When you are done, :q out of the diff buffers and :LinediffReset to get rid of the range specifiers in the original buffers.

The Stackoverflow answer where I first learned of linediff.vim also suggests a couple of mappings. Other answers on that question also mention a custom solution and another plugin that can address this same issue.

Related Solutions

Vimdiff: Jump to next difference inside line

I see two solutions:

you would have to test the current syntax highlighting to jump to the red part in the line.
you would have to extract the current line in both buffers and find the first character that differs to position correctly the cursor

Both solutions need to be executed after the ]c, and require vim scripting.

EDIT: Here is a first draft that seems to work:

nnoremap <expr> <silent> <F3>   (&diff ? "]c:call \<sid>NextDiff()\<cr>" : ":cn\<cr>")

function! s:GotoWinline(w_l)
  normal! H
  while winline() < a:w_l
    normal! j
  endwhile
  " todo: beware of cases where the window is too little
endfunction

" Better ]c, [c jump
function! s:NextDiff()
  if ! &diffopt =~ 'filler' | return | endif

  let ignore_blanks = &diffopt =~ 'iwhite'

  " Assert: called just after a ]c or a [c
  " Forces the cursos to be synchronized in all synced windows
  " let diff_l = line()
  try 
    let foldenable = &foldenable
    set nofoldenable

    let w_l = winline() " problematic with enabled lines (from diff...)
    " echomsg w_l.'|'.line('.').'|'.getline('.')

    let lines = {}
    windo if &diff | call <sid>GotoWinline(w_l) | let lines[winnr()]={'text':getline('.'), 'number':line('.')} | endif
  finally
    let &foldenable = foldenable
  endtry

  " echomsg string(lines)
  if len(lines) < 2 | return | endif

  let indices = repeat([0], len(lines))
  let tLines = values(lines)
  let found = 0
  " infinite loop on two empty texts...
  while ! found
    let c = ''
    let next_idx = []
    let i = 0
    while i != len(indices)
      let crt_line = tLines[i].text
      let n = indices[i]
      if len(crt_line) == n
    let found = 1
    break
      endif

      let c2 = (len(crt_line) == n) ? 'EOL' : crt_line[n]
      if empty(c) 
    let c = c2
      endif

      " checks match
      let n += 1
      if c =~ '\s'
    if (c2 != c) && (ignore_blanks && c2 !~ '\s')
      let found = 1
      break
    else " advance
      while ignore_blanks && (n == len(crt_line) || crt_line[n] =~ '\s')
        let n += 1
      endwhile
    endif
      else
    if c2 != c
      let found = 1
      break
    endif
      endif
      let next_idx += [n]

      let i += 1
    endwhile
    if found | break | endif

    let indices = next_idx
  endwhile

  " now goto the right column
  let windows = keys(lines)
  " Assert len(windows) == len(indices)
  let w = 0
  while w != len(windows)
    " echomsg 'W#'.windows[w].' -> :'(tLines[w].number).'normal! '.(indices[w]+1).'|'
    exe windows[w].'wincmd w'
    silent! exe (tLines[w].number).'normal! 0'.(indices[w]).'l'
    let w += 1
  endwhile
  " echomsg string(indices)
endfunction

Mac – How to only dp or do just the lines, not the entire block in Vim diff

There are a number of ways to do this.

Select the range of lines in the destination buffer that you want to obtain from the source buffer and use :diffget. For example, you could visually-select a range of lines with V, then type :diffget.
Select the range of lines in the source buffer that you want to put into the destination buffer and use :diffput. For example, to put the current line into the other buffer, type :.diffput.
Use yank and put. Select the range of lines in the source buffer that you want to copy into the destination buffer, yank them using Y, move the cursor to the destination buffer and put them where you want them with p or P, then delete the lines you don't want.
Yank as above, but in the destination buffer, visually-select the range of lines you want to replace (not necessarily the same number of lines) and type "0p. That uses the 0 (zero) register which always contains the text of the most recent yank.

To "refresh" the display to show the proper highlighting, execute :diffupdate or simply :diffu. Sometimes that isn't sufficient and you need to move the cursor to the other window to complete the refreshing.

You can read more about copying diffs in

:help copy-diffs

Best Answer

Related Solutions

Vimdiff: Jump to next difference inside line

Mac – How to only dp or do just the lines, not the entire block in Vim diff

Related Question