# Vim documentation: diff

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    *diff.txt*      For Vim version 6.1.  Last change: 2002 Mar 09

    		  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 -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.  Thus when splitting the window or
    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
    	else
    	   setup for non-diff mode
    	endif

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

    							*E98*

    :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

    							*E96*
    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
    	:set 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.

    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 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
    buffer.

    							*: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:

    	:diffupdate

    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.
    |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*

    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
    		mode.
    		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*
    do		Same as ":diffget" without argument or range.  The "o" stands
    		for "obtain" ("dg" can't be used for this!).

    							*dp*
    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.

    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")

    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.

    There can be deleted lines below the last line of the buffer.  To be able to
    get those lines from another buffer it's allowed to use the last line number
    plus one.  This command gets all diffs from the other buffer:

    	:1,$+1diffget

    ==============================================================================

    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:

    	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 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.

    Example (this does the same as 'diffexpr' being empty, but adds the "-a"
    flag to force comparing them as text):

    	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 " . opt . v:fname_in . " " . v:fname_new .
    		\  " > " . v:fname_out
    	endfunction

    						*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.

    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)
    	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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