[git] Git: How configure KDiff3 as merge tool and diff tool

Recently I was using GitExtension 2.46, but the Git version that has the same is 1.9.4.msysgit.2. Willing to use only Git commands, I uninstalled GitExtension and install the latest version available of Git and KDiff3.

When I make a merge and have conflicts, I run the following command:

$ git mergetool

Then I receive the message:

The merge tool kdiff3 is not available as 'kdiff3'.

I guess it must be by the KDiff3 path.

Environment

• OS: Windows 10
• Git 2.6.1.windows.1
• KDiff3 0.9.98 (64 bit)

Questions:

• What do I have to configure in the .gitconfig file for the command $ git mergetool to open the KDiff3 GUI with the versions LOCAL, REMOTE, BASE and MERGED of conflicted file?

• How configure it to use it has diff-tool?

Just to extend the @Joseph's answer:

After applying these commands your global .gitconfig file will have the following lines (to speed up the process you can just copy them in the file):

[merge]
    tool = kdiff3
[mergetool "kdiff3"]
    path = C:/Program Files/KDiff3/kdiff3.exe
    trustExitCode = false
[diff]
    guitool = kdiff3
[difftool "kdiff3"]
    path = C:/Program Files/KDiff3/kdiff3.exe
    trustExitCode = false

I needed to add the command line parameters or KDiff3 would only open without files and prompt me for base, local and remote. I used the version supplied with TortoiseHg.

Additionally, I needed to resort to the good old DOS 8.3 file names.

[merge]
    tool = kdiff3

[mergetool "kdiff3"]
    cmd = /c/Progra~1/TortoiseHg/lib/kdiff3.exe $BASE $LOCAL $REMOTE -o $MERGED

However, it works correctly now.

Well, the problem is that Git can't find KDiff3 in the %PATH%.

In a typical Unix installation all executables reside in several well-known locations (/bin/, /usr/bin/, /usr/local/bin/, etc.), and one can invoke a program by simply typing its name in a shell processor (e.g. cmd.exe :) ).

In Microsoft Windows, programs are usually installed in dedicated paths so you can't simply type kdiff3 in a cmd session and get KDiff3 running.

The hard solution: you should tell Git where to find KDiff3 by specifying the full path to kdiff3.exe. Unfortunately, Git doesn't like spaces in the path specification in its config, so the last time I needed this, I ended up with those ancient "C:\Progra~1...\kdiff3.exe" as if it was late 1990s :)

The simple solution: Edit your computer settings and include the directory with kdiff3.exe in %PATH%. Then test if you can invoke it from cmd.exe by its name and then run Git.

For Mac users

Here is @Joseph's accepted answer, but with the default Mac install path location of kdiff3

(Note that you can copy and paste this and run it in one go)

git config --global --add merge.tool kdiff3 
git config --global --add mergetool.kdiff3.path  "/Applications/kdiff3.app/Contents/MacOS/kdiff3" 
git config --global --add mergetool.kdiff3.trustExitCode false

git config --global --add diff.guitool kdiff3
git config --global --add difftool.kdiff3.path "/Applications/kdiff3.app/Contents/MacOS/kdiff3"
git config --global --add difftool.kdiff3.trustExitCode false

To amend kris' answer, starting with Git 2.20 (Q4 2018), the proper command for git mergetool will be

git config --global merge.guitool kdiff3 

That is because "git mergetool" learned to take the "--[no-]gui" option, just like "git difftool" does.

See commit c217b93, commit 57ba181, commit 063f2bd (24 Oct 2018) by Denton Liu (Denton-L).
^{(Merged by Junio C Hamano -- gitster -- in commit 87c15d1, 30 Oct 2018)}

mergetool: accept -g/--[no-]gui as arguments

In line with how difftool accepts a -g/--[no-]gui option, make mergetool accept the same option in order to use the merge.guitool variable to find the default mergetool instead of merge.tool.

(When trying to find out how to use kdiff3 from WSL git I ended up here and got the final pieces, so I'll post my solution for anyone else also stumbling in here while trying to find that answer)

How to use kdiff3 as diff/merge tool for WSL git

With Windows update 1903 it is a lot easier; just use wslpath and there is no need to share TMP from Windows to WSL since the Windows side now has access to the WSL filesystem via \wsl$:

[merge]
    renormalize = true
    guitool = kdiff3
[diff]
    tool = kdiff3
[difftool]
    prompt = false
[difftool "kdiff3"]
    # Unix style paths must be converted to windows path style
    cmd = kdiff3.exe \"`wslpath -w $LOCAL`\" \"`wslpath -w $REMOTE`\"
    trustExitCode = false
[mergetool]
    keepBackup = false
    prompt = false
[mergetool "kdiff3"]
    path = kdiff3.exe
    trustExitCode = false

Before Windows update 1903

Steps for using kdiff3 installed on Windows 10 as diff/merge tool for git in WSL:

1. Add the kdiff3 installation directory to the Windows Path.
2. Add TMP to the WSLENV Windows environment variable (WSLENV=TMP/up). The TMP dir will be used by git for temporary files, like previous revisions of files, so the path must be on the windows filesystem for this to work.
3. Set TMPDIR to TMP in .bashrc:

# If TMP is passed via WSLENV then use it as TMPDIR
[[ ! -z "$WSLENV" && ! -z "$TMP" ]] && export TMPDIR=$TMP

4. Convert unix-path to windows-path when calling kdiff3. Sample of my .gitconfig:

[merge]
    renormalize = true
    guitool = kdiff3
[diff]
    tool = kdiff3
[difftool]
    prompt = false
[difftool "kdiff3"]
    #path = kdiff3.exe
    # Unix style paths must be converted to windows path style by changing '/mnt/c/' or '/c/' to 'c:/'
    cmd = kdiff3.exe \"`echo $LOCAL | sed 's_^\\(/mnt\\)\\?/\\([a-z]\\)/_\\2:/_'`\" \"`echo $REMOTE | sed 's_^\\(/mnt\\)\\?/\\([a-z]\\)/_\\2:/_'`\"
    trustExitCode = false
[mergetool]
    keepBackup = false
    prompt = false
[mergetool "kdiff3"]
    path = kdiff3.exe
    trustExitCode = false