Diff

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diff-mode This file describes the diff feature: Showing differences between two to eight versions of the same file.
The basics are explained in section 08.7 of the user manual.

1. Starting diff mode start-vimdiff

To start editing in diff mode, run "nvim -d". This starts Nvim as usual, and additionally sets up for viewing the differences between the arguments.
nvim -d file1 file2 [file3 [file4]]
In addition to the -d argument, -R may be used for readonly mode.
The second and following arguments may also be a directory name. Vim will then append the file name of the first argument to the directory name to find the file.
By default an internal diff library will be used. When 'diffopt' or 'diffexpr' has been set an external "diff" command will be used. This only works when such a diff program is available.
Diffs are local to the current tab page tab-page. You can't see diffs with a window in another tab page. This does make it possible to have several diffs at the same time, each in their own tab page.
What happens is that Nvim opens a window for each of the files. This is like using the -O argument. This uses vertical splits, but if you prefer horizontal splits use the -o argument instead:
nvim -d -o file1 file2 [file3 [file4]]
If you always prefer horizontal splits include "horizontal" in 'diffopt'.
In each of the edited files these options are set:
'diff' on 'scrollbind' on 'cursorbind' on 'scrollopt' includes "hor" 'wrap' off, or leave as-is if 'diffopt' includes "followwrap" 'foldmethod' "diff" 'foldcolumn' value from 'diffopt', default is 2
These options are set local to the window. When editing another file they are reset to the global value. The options can still be overruled from a modeline when re-editing the file. However, 'foldmethod' and 'wrap' won't be set from a modeline when 'diff' is set. See :diffoff for an easy way to revert the options.
The differences shown are actually the differences in the buffer. Thus if you make changes after loading a file, these will be included in the displayed diffs. You might have to do ":diffupdate" now and then, not all changes are immediately taken into account, especially when using an external diff command.
In your vimrc file you could do something special when Vim was started in diff mode. You could use a construct like this:
if &diff
   setup for diff mode
else
   setup for non-diff mode
endif
While already in Vim you can start diff mode in three ways.
E98 :diffs[plit] {filename} :diffs :diffsplit Open a new window on the file {filename}. The options are set as for "nvim -d" for the current and the newly opened window. Also see 'diffexpr'.
:difft :diffthis :difft[his] Make the current window part of the diff windows. This sets the options as for "nvim -d".
:diffp[atch] {patchfile} E816 :diffp :diffpatch Use the current buffer, patch it with the diff found in {patchfile} and open a buffer on the result. This sets the options as for "nvim -d". {patchfile} can be in any format that the "patch" program understands or 'patchexpr' can handle. Note that {patchfile} should only contain a diff for one file, the current file. If {patchfile} contains diffs for other files as well, the results are unpredictable. Vim changes directory to /tmp to avoid files in the current directory accidentally being patched. But it may still result in various ".rej" files to be created. And when absolute path names are present these files may get patched anyway.
To make these commands use a vertical split, prepend :vertical. Examples:
:vert diffsplit main.c~
:vert diffpatch /tmp/diff
If you always prefer a vertical split include "vertical" in 'diffopt'.
E96 There can be up to eight buffers with 'diff' set.
Since the option values are remembered with the buffer, you can edit another file for a moment and come back to the same file and be in diff mode again.
:diffo :diffoff :diffo[ff] Switch off diff mode for the current window. Resets related options also when 'diff' was not set.
:diffo[ff]! Switch off diff mode for the current window and in all windows in the current tab page where 'diff' is set. Resetting related options only happens in a window that has 'diff' set, if the current window does not have 'diff' set then no options in it are changed. Hidden buffers are also removed from the list of diff'ed buffers.
The :diffoff command resets the relevant options to the values they had when using :diffsplit, :diffpatch , :diffthis. or starting Vim in diff mode. When using :diffoff twice the last saved values are restored. Otherwise they are set to their default value:
'diff' off 'scrollbind' off 'cursorbind' off 'scrollopt' without "hor" 'wrap' on, or leave as-is if 'diffopt' includes "followwrap" 'foldmethod' "manual" 'foldcolumn' 0

2. Viewing diffs view-diffs

The effect is that the diff windows show the same text, with the differences highlighted. When scrolling the text, the 'scrollbind' option will make the text in other windows to be scrolled as well. With vertical splits the text should be aligned properly.
The alignment of text will go wrong when:
'wrap' is on, some lines will be wrapped and occupy two or more screen lines
folds are open in one window but not another
'scrollbind' is off
changes have been made to the text
"filler" is not present in 'diffopt', deleted/inserted lines makes the alignment go wrong
All the buffers edited in a window where the 'diff' option is set will join in the diff. This is also possible for hidden buffers. They must have been edited in a window first for this to be possible. To get rid of the hidden buffers use :diffoff!.
:DiffOrig diff-original-file Since 'diff' is a window-local option, it's possible to view the same buffer in diff mode in one window and "normal" in another window. It is also possible to view the changes you have made to a buffer since the file was loaded. Since Vim doesn't allow having two buffers for the same file, you need another buffer. This command is useful:
command DiffOrig vert new | set buftype=nofile | read ++edit # | 0d_
       \ | diffthis | wincmd p | diffthis
Use ":DiffOrig" to see the differences between the current buffer and the file it was loaded from.
A buffer that is unloaded cannot be used for the diff. But it does work for hidden buffers. You can use ":hide" to close a window without unloading the buffer. If you don't want a buffer to remain used for the diff do ":set nodiff" before hiding it.
:dif :diff :diffupdate :dif[fupdate][!] Update the diff highlighting and folds.
Vim attempts to keep the differences updated when you make changes to the text. This mostly takes care of inserted and deleted lines. Changes within a line and more complicated changes do not cause the differences to be updated. To force the differences to be updated use:
:diffupdate
If the ! is included Vim will check if the file was changed externally and needs to be reloaded. It will prompt for each changed file, like :checktime was used.
Vim will show filler lines for lines that are missing in one window but are present in another. These lines were inserted in another file or deleted in this file. Removing "filler" from the 'diffopt' option will make Vim not display these filler lines.
Folds are used to hide the text that wasn't changed. See folding for all the commands that can be used with folds.
The context of lines above a difference that are not included in the fold can be set with the 'diffopt' option. For example, to set the context to three lines:
:set diffopt=filler,context:3
The diffs are highlighted with these groups:
hl-DiffAdd DiffAdd Added (inserted) lines. These lines exist in this buffer but not in another. hl-DiffChange DiffChange Changed lines. hl-DiffText DiffText Changed text inside a Changed line. Vim finds the first character that is different, and the last character that is different (searching from the end of the line). The text in between is highlighted. This means that parts in the middle that are still the same are highlighted anyway. The 'diffopt' flags "iwhite" and "icase" are used here. hl-DiffDelete DiffDelete Deleted lines. Also called filler lines, because they don't really exist in this buffer.

3. Jumping to diffs jumpto-diffs

Two commands can be used to jump to diffs: [c [c Jump backwards to the previous start of a change. When a count is used, do it that many times. ]c ]c Jump forwards to the next start of a change. When a count is used, do it that many times.
It is an error if there is no change for the cursor to move to.

4. Diff copying copy-diffs E99 E100 E101 E102 E103

merge There are two commands to copy text from one buffer to another. The result is that the buffers will be equal within the specified range.
:diffg :diffget :[range]diffg[et] [bufspec] Modify the current buffer to undo difference with another buffer. If [bufspec] is given, that buffer is used. If [bufspec] refers to the current buffer then nothing happens. Otherwise this only works if there is one other buffer in diff mode. See below for [range].
:diffpu :diffput E793 :[range]diffpu[t] [bufspec] Modify another buffer to undo difference with the current buffer. Just like ":diffget" but the other buffer is modified instead of the current one. When [bufspec] is omitted and there is more than one other buffer in diff mode where 'modifiable' is set this fails. See below for [range].
do [count]do Same as ":diffget" without range. The "o" stands for "obtain" ("dg" can't be used, it could be the start of "dgg"!). Note: this doesn't work in Visual mode. If you give a [count], it is used as the [bufspec] argument for ":diffget".
dp [count]dp Same as ":diffput" without range. Note: this doesn't work in Visual mode. If you give a [count], it is used as the [bufspec] argument for ":diffput".
When no [range] is given, the diff at the cursor position or just above it is affected. When [range] is used, Vim tries to only put or get the specified lines. When there are deleted lines, this may not always be possible.
There can be deleted lines below the last line of the buffer. When the cursor is on the last line in the buffer and there is no diff above this line, the ":diffget" and "do" commands will obtain lines from the other buffer.
To be able to get those lines from another buffer in a [range] it's allowed to use the last line number plus one. This command gets all diffs from the other buffer:
:1,$+1diffget
Note that deleted lines are displayed, but not counted as text lines. You can't move the cursor into them. To fill the deleted lines with the lines from another buffer use ":diffget" on the line below them. E787 When the buffer that is about to be modified is read-only and the autocommand that is triggered by FileChangedRO changes buffers the command will fail. The autocommand must not change buffers.
The [bufspec] argument above can be a buffer number, a pattern for a buffer name or a part of a buffer name. Examples:
:diffget Use the other buffer which is in diff mode :diffget 3 Use buffer 3 :diffget v2 Use the buffer which matches "v2" and is in diff mode (e.g., "file.c.v2")

5. Diff options diff-options

Also see 'diffopt' and the "diff" item of 'fillchars'.
diff-slow diff_translations For very long lines, the diff syntax highlighting might be slow, especially since it tries to match all different kind of localisations. To disable localisations and speed up the syntax highlighting, set the global variable g:diff_translations to zero:
let g:diff_translations = 0
After setting this variable, reload the syntax script:
set syntax=diff

FINDING THE DIFFERENCES diff-diffexpr

The 'diffexpr' option can be set to use something else than the internal diff support or the standard "diff" program to compare two files and find the differences.
When 'diffexpr' is empty, Vim uses this command to find the differences between file1 and file2:
diff file1 file2 > outfile
The ">" is replaced with the value of 'shellredir'.
The output of "diff" must be a normal "ed" style diff or a unified diff. A context diff will NOT work. For a unified diff no context lines can be used. Using "diff -u" will NOT work, use "diff -U0".
This example explains the format that Vim expects for the "ed" style diff:
1a2
> bbb
4d4
< 111
7c7
< GGG
---
> ggg
The "1a2" item appends the line "bbb". The "4d4" item deletes the line "111". The "7c7" item replaces the line "GGG" with "ggg".
When 'diffexpr' is not empty, Vim evaluates it to obtain a diff file in the format mentioned. These variables are set to the file names used:
v:fname_in original file v:fname_new new version of the same file v:fname_out where to write the resulting diff file
Additionally, 'diffexpr' should take care of "icase" and "iwhite" in the 'diffopt' option. 'diffexpr' cannot change the value of 'lines' and 'columns'.
Example (this does almost the same as 'diffexpr' being empty):
set diffexpr=MyDiff()
function MyDiff()
   let opt = ""
   if &diffopt =~ "icase"
     let opt = opt .. "-i "
   endif
   if &diffopt =~ "iwhite"
     let opt = opt .. "-b "
   endif
   silent execute "!diff -a --binary " .. opt .. v:fname_in .. " " .. v:fname_new ..
        \  " > " .. v:fname_out
   redraw!
endfunction
The "-a" argument is used to force comparing the files as text, comparing as binaries isn't useful. The "--binary" argument makes the files read in binary mode, so that a CTRL-Z doesn't end the text on DOS.
The redraw! command may not be needed, depending on whether executing a shell command shows something on the display or not.
E810 E97 Vim will do a test if the diff output looks alright. If it doesn't, you will get an error message. Possible causes:
The "diff" program cannot be executed.
The "diff" program doesn't produce normal "ed" style diffs (see above).
The 'shell' and associated options are not set correctly. Try if filtering works with a command like ":!sort".
You are using 'diffexpr' and it doesn't work. If it's not clear what the problem is set the 'verbose' option to one or more to see more messages.
The self-installing Vim for MS-Windows includes a diff program. If you don't have it you might want to download a diff.exe. For example from https://gnuwin32.sourceforge.net/packages/diffutils.htm.

USING PATCHES diff-patchexpr

The 'patchexpr' option can be set to use something else than the standard "patch" program.
When 'patchexpr' is empty, Vim will call the "patch" program like this:
patch -o outfile origfile < patchfile
This should work fine with most versions of the "patch" program. Note that a CR in the middle of a line may cause problems, it is seen as a line break.
If the default doesn't work for you, set the 'patchexpr' to an expression that will have the same effect. These variables are set to the file names used:
v:fname_in original file v:fname_diff patch file v:fname_out resulting patched file
Example (this does the same as 'patchexpr' being empty):
set patchexpr=MyPatch()
function MyPatch()
   :call system("patch -o " .. v:fname_out .. " " .. v:fname_in ..
   \  " < " .. v:fname_diff)
endfunction
Make sure that using the "patch" program doesn't have unwanted side effects. For example, watch out for additionally generated files, which should be deleted. It should just patch the file and nothing else. Vim will change directory to "/tmp" or another temp directory before evaluating 'patchexpr'. This hopefully avoids that files in the current directory are accidentally patched. Vim will also delete files starting with v:fname_in and ending in ".rej" and ".orig".
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