How do I view 'git diff' output with my preferred diff tool/ viewer?

Question

When I type git diff, I want to view the output with my visual diff tool of choice (SourceGear "diffmerge" on Windows). How do I configure git to do this?

VonC_6309 · Answer

Since Git1.6.3, you can use the git difftool script: see my answer below.

May be this article will help you. Here are the best parts:

There are two different ways to specify an external diff tool.

The first is the method you used, by setting the GIT_EXTERNAL_DIFF variable. However, the variable is supposed to point to the full path of the executable. Moreover, the executable specified by GIT_EXTERNAL_DIFF will be called with a fixed set of 7 arguments:

path old-file old-hex old-mode new-file new-hex new-mode

As most diff tools will require a different order (and only some) of the arguments, you will most likely have to specify a wrapper script instead, which in turn calls the real diff tool.

The second method, which I prefer, is to configure the external diff tool via "git config". Here is what I did:

1) Create a wrapper script "git-diff-wrapper.sh" which contains something like

-->8-(snip)--
#!/bin/sh

# diff is called by git with 7 parameters:
# path old-file old-hex old-mode new-file new-hex new-mode

"" "$2" "$5" | cat
--8<-(snap)--

As you can see, only the second ("old-file") and fifth ("new-file") arguments will be passed to the diff tool.

2) Type

$ git config --global diff.external

at the command prompt, replacing with the path to "git-diff-wrapper.sh", so your ~/.gitconfig contains

-->8-(snip)--
[diff]
    external = 
--8<-(snap)--

Be sure to use the correct syntax to specify the paths to the wrapper script and diff tool, i.e. use forward slashed instead of backslashes. In my case, I have

[diff]
    external = \"c:/Documents and Settings/sschuber/git-diff-wrapper.sh\"

in .gitconfig and

"d:/Program Files/Beyond Compare 3/BCompare.exe" "$2" "$5" | cat

in the wrapper script. Mind the trailing "cat"!

(I suppose the '| cat' is needed only for some programs which may not return a proper or consistent return status. You might want to try without the trailing cat if your diff tool has explicit return status)

(Diomidis Spinellis adds in the comments:

The cat command is required, because diff(1), by default exits with an error code if the files differ.
Git expects the external diff program to exit with an error code only if an actual error occurred, e.g. if it run out of memory.
By piping the output of git to cat the non-zero error code is masked.
More efficiently, the program could just run exit with and argument of 0.)

That (the article quoted above) is the theory for external tool defined through config file (not through environment variable).
In practice (still for config file definition of external tool), you can refer to:

How do I setup DiffMerge with msysgit / gitk? which illustrates the concrete settings of DiffMerge and WinMerge for MsysGit and gitk
How can I set up an editor to work with Git on Windows? for the definition of Notepad++ as an external editor.

VonC_6309 · Answer

To complete my previous "diff.external" config answer above:

As mentioned by Jakub, Git1.6.3 introduced git difftool, originally proposed in September 2008:

USAGE='[--tool=tool] [--commit=ref] [--start=ref --end=ref] [--no-prompt] [file to merge]'
(See --extcmd in the last part of this answer)

$LOCAL contains the contents of the file from the starting revision and $REMOTE contains the contents of the file in the ending revision.
$BASE contains the contents of the file in the wor

It's basically git-mergetool modified to operate on the git index/worktree.

The usual use case for this script is when you have either staged or unstaged changes and you'd like to see the changes in a side-by-side diff viewer (e.g. xxdiff, tkdiff, etc).

git difftool [*]

Another use case is when you'd like to see the same information but are comparing arbitrary commits (this is the part where the revarg parsing could be better)

git difftool --start=HEAD^ --end=HEAD [-- *]

The last use case is when you'd like to compare your current worktree to something other than HEAD (e.g. a tag)

git difftool --commit=v1.0.0 [-- *]

Note: since Git 2.5, git config diff.tool winmerge is enough!
See "git mergetool winmerge"

And since Git 1.7.11, you have the option --dir-diff, in order to to spawn external diff tools that can compare two directory hierarchies at a time after populating two temporary directories, instead of running an instance of the external tool once per a file pair.

Before Git 2.5:

Practical case for configuring difftool with your custom diff tool:

C:\myGitRepo>git config --global diff.tool winmerge
C:\myGitRepo>git config --global difftool.winmerge.cmd "winmerge.sh \"$LOCAL\" \"$REMOTE\""
C:\myGitRepo>git config --global difftool.prompt false

With winmerge.sh stored in a directory part of your PATH:

#!/bin/sh
echo Launching WinMergeU.exe: $1 $2
"C:/Program Files/WinMerge/WinMergeU.exe" -u -e "$1" "$2" -dl "Local" -dr "Remote"

If you have another tool (kdiff3, P4Diff, ...), create another shell script, and the appropriate difftool.myDiffTool.cmd config directive.
Then you can easily switch tools with the diff.tool config.

You have also this blog entry by Dave to add other details.
(Or this question for the winmergeu options)

The interest with this setting is the winmerge.shscript: you can customize it to take into account special cases.

See for instance David Marble's answer below for an example which deals with:

new files in either origin or destination
removed files in either origin or destination

As Kem Mason mentions in his answer, you can also avoid any wrapper by using the --extcmd option:

--extcmd=

Specify a custom command for viewing diffs. git-difftool ignores the configured defaults and runs $command $LOCAL $REMOTE when this option is specified.

For instance, this is how gitk is able to run/use any diff tool.

user_1320510 · Answer

Try this solution:

$ meld my_project_using_git

Meld understands Git and provides navigating around the recent changes.

user_46058 · Answer

Since Git version 1.6.3 there is "git difftool" which you can configure to use your favorite graphical diff tool.

Currently supported (at the time of writing this answer) out-of-the-box are KDiff3, Kompare, tkdiff, Meld, xxdiff, emerge, vimdiff, gvimdiff, ecmerge, Diffuse and opendiff; if the tool you want to use isn't on this list, you can always use 'difftool..cmd' configuration option.

"git difftool" accepts the same options as "git diff".

user_398582 · Answer

I have one addition to this. I like to regularly use a diff app that isn't supported as one of the default tools (e.g. kaleidoscope), via

git difftool -t

I also like to have the default diff just be the regular command line, so setting the GIT_EXTERNAL_DIFF variable isn't an option.

You can use an arbitrary diff app as a one-off with this command:

git difftool --extcmd=/usr/bin/ksdiff

It just passes the 2 files to the command you specify, so you probably don't need a wrapper either.

user_15947 · Answer

Solution for Windows/MSYS Git

After reading the answers, I discovered a simpler way that involves changing only one file.

Create a batch file to invoke your diff program, with argument 2 and 5. This file must be somewhere in your path. (If you don't know where that is, put it in C:\windows.) Call it, for example, "gitdiff.bat". Mine is:
```
@echo off
REM This is gitdiff.bat
"C:\Program Files\WinMerge\WinMergeU.exe" %2 %5
```
Set the environment variable to point to your batch file. For example:GIT_EXTERNAL_DIFF=gitdiff.bat. Or through PowerShell by typing git config --global diff.external gitdiff.bat.

It is important to not use quotes, or specify any path information, otherwise it won't work. That's why gitdiff.bat must be in your path.

Now when you type "git diff", it will invoke your external diff viewer.

MilanG_23843 · Answer

Introduction

For reference I'd like to include my variation on VonC's answer. Keep in mind that I am using the MSys version of Git (1.6.0.2 at this time) with modified PATH, and running Git itself from PowerShell (or cmd.exe), not the Bash shell.

I introduced a new command, gitdiff. Running this command temporarily redirects git diff to use a visual diff program of your choice (as opposed to VonC's solution that does it permanently). This allows me to have both the default Git diff functionality (git diff) as well as visual diff functionality (gitdiff). Both commands take the same parameters, so for example to visually diff changes in a particular file you can type

gitdiff path/file.txt

Setup

Note that $GitInstall is used as a placeholder for the directory where Git is installed.

Create a new file, $GitInstall\cmd\gitdiff.cmd

 @echo off
 setlocal
 for /F "delims=" %%I in ("%~dp0..") do @set path=%%~fI\bin;%%~fI\mingw\bin;%PATH%
 if "%HOME%"=="" @set HOME=%USERPROFILE%
 set GIT_EXTERNAL_DIFF=git-diff-visual.cmd
 set GIT_PAGER=cat
 git diff %*
 endlocal

Create a new file, $GitInstall\bin\git-diff-visual.cmd (replacing [visual_diff_exe] placeholder with full path to the diff program of your choice)

 @echo off
 rem diff is called by git with 7 parameters:
 rem path old-file old-hex old-mode new-file new-hex new-mode
 echo Diffing "%5"
 "[visual_diff_exe]" "%2" "%5"
 exit 0

You're now done. Running gitdiff from within a Git repository should now invoke your visual diff program for every file that was changed.

user_77002 · Answer

Here's a batch file that works for Windows - assumes DiffMerge installed in default location, handles x64, handles forward to backslash replacement as necessary and has ability to install itself. Should be easy to replace DiffMerge with your favourite diff program.

To install:

gitvdiff --install

gitvdiff.bat:

@echo off

REM ---- Install? ----
REM To install, run gitvdiff --install

if %1==--install goto install



REM ---- Find DiffMerge ----

if DEFINED ProgramFiles^(x86^) (
    Set DIFF="%ProgramFiles(x86)%\SourceGear\DiffMerge\DiffMerge.exe"
) else (
    Set DIFF="%ProgramFiles%\SourceGear\DiffMerge\DiffMerge.exe"
)



REM ---- Switch forward slashes to back slashes ----

set oldW=%2
set oldW=%oldW:/=\%
set newW=%5
set newW=%newW:/=\%


REM ---- Launch DiffMerge ----

%DIFF% /title1="Old Version" %oldW% /title2="New Version" %newW%

goto :EOF



REM ---- Install ----
:install
set selfL=%~dpnx0
set selfL=%selfL:\=/%
@echo on
git config --global diff.external %selfL%
@echo off


:EOF

user_1429266 · Answer

The following can be gleaned from the other answers here, but for me it's difficult, (too much information), so here's the 'just type it in' answer for tkdiff:

git difftool --tool=tkdiff

You can substitute the executable name of your favorite diffing tool for tkdiff. As long as (e.g. tkdiff), (or your favorite diffing tool) is in your PATH, it will be launched.

user_3068121 · Answer

I tried the fancy stuff here (with tkdiff) and nothing worked for me. So I wrote the following script, tkgitdiff. It does what I need it to do.

$ cat tkgitdiff
#!/bin/sh

#
# tkdiff for git.
# Gives you the diff between HEAD and the current state of your file.
#

newfile=$1
git diff HEAD -- $newfile > /tmp/patch.dat
cp $newfile /tmp
savedPWD=$PWD
cd /tmp
patch -R $newfile < patch.dat
cd $savedPWD
tkdiff /tmp/$newfile $newfile

user_253511 · Answer

I use Kompare on Ubuntu:

sudo apt-get install kompare

To compare two branches:

git difftool -t kompare  master

How do I view 'git diff' output with my preferred diff tool/ viewer?

26 Answers

Solution for Windows/MSYS Git

Introduction

Setup