Vim documentation: diff

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*diff.txt*      For Vim version 6.3.  Last change: 2004 May 01

		  VIM REFERENCE MANUAL    by Bram Moolenaar

				*diff* *vimdiff* *gvimdiff* *diff-mode*
This file describes the +diff feature: Showing differences between two or
three versions of the same file.

The basics are explained in section |08.7| of the user manual.

1. Starting diff mode		|vimdiff|
2. Viewing diffs		|view-diffs|
3. Jumping to diffs		|jumpto-diffs|
4. Copying diffs		|copy-diffs|
5. Diff options			|diff-options|

{not in Vi}

1. Starting diff mode

The easiest way to start editing in diff mode is with the "vimdiff" command.
This starts Vim as usual, and additionally sets up for viewing the differences
between the arguments.

	vimdiff file1 file2 [file3 [file4]]

This is equivalent to:

	vim -d file1 file2 [file3 [file4]]

You may also use "gvimdiff" or "vim -d -g".  The GUI is started then.
You may also use "viewdiff" or "gviewdiff".  Vim starts in readonly mode then.
"r" may be prepended for restricted mode (see |-Z|).

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.

This only works when a standard "diff" command is available.  See 'diffexpr'.

What happens is that Vim opens a window for each of the files.  This is like
using the |-O| argument.  This uses vertical splits.  If you prefer horizontal
splits add the |-o| argument:

	vimdiff -o file1 file2 [file3]

In each of the edited files these options are set:

	'diff'		on
	'scrollbind'	on
	'scrollopt'	includes "hor"
	'wrap'		off
	'foldmethod'	"diff"
	'foldcolumn'	2

These options are set local to the window.  When editing another file they are
reset to the global value.

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.

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
	   setup for non-diff mode

While already in Vim you can start diff mode in three ways.


:diffsplit {filename}					*:diffs* *:diffsplit*
		Open a new window on the file {filename}.  The options are set
		as for "vimdiff" for the current and the newly opened window.
		Also see 'diffexpr'.

							*:difft* *:diffthis*
:diffthis	Make the current window part of the diff windows.  This sets
		the option like for "vimdiff".

:diffpatch {patchfile}					*:diffp* *:diffpatch*
		Use the current buffer, patch it with the diff found in
		{patchfile} and open a buffer on the result.  The options are
		set as for "vimdiff".
		{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

There can be up to four 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.
If you don't want diff mode, reset the 'diff' option.  And you probably want
to get rid of the fold column:

	:set nodiff 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
- 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.

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, but since Vim doesn't
allow having two buffers for the same file, you need to make a copy of the
original file and diff with that.  For example:
	:!cp % tempfile
	:diffsplit tempfile

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

							*:diffu* *:diffupdate*
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:


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

	: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.
|hl-DiffDelete| DiffDelete	Deleted lines.  Also called filler lines,
				because they don't really exist in this


3. Jumping to diffs					*jumpto-diffs*

Two commands can be used to jump to diffs:

	[c		Jump backwards to the previous start of a change.
			When a count is used, do it that many times.

	]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*

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.
		Otherwise this only works if there is one other buffer in diff
		See below for [range].

							*:diffpu* *:diffput*
:[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.
		See below for [range].

do		Same as ":diffget" without argument or range.  The "o" stands
		for "obtain" ("dg" can't be used, it could be the start of

dp		Same as ":diffput" without argument or range.

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


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.

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'|.

FINDING THE DIFFERENCES					*diff-diffexpr*

The 'diffexpr' option can be set to use something else than 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.  Do NOT use a context
diff.  This example explains the format that Vim expects:

	> bbb
	< 111
	< 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 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		resulting diff file

Additionally, 'diffexpr' should take care of "icase" and "iwhite" in the
'diffopt' option.  'diffexpr' cannot change the value of 'lines' and

Example (this does almost the same as 'diffexpr' being empty):

	set diffexpr=MyDiff()
	function MyDiff()
	   let opt = ""
	   if &diffopt =~ "icase"
	     let opt = opt . "-i "
	   if &diffopt =~ "iwhite"
	     let opt = opt . "-b "
	   silent execute "!diff -a --binary " . opt . v:fname_in . " " . v:fname_new .
		\  " > " . v:fname_out

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.

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 see more

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):

	let patchexpr=MyPatch
	function MyPatch
	   :call system("patch -o " . v:fname_out . " " . v:fname_in .
	   \  " < " . v:fname_diff)

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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