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Git - External merge and difftools
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  Setting up Beyond Compare

You can set the path to bcomp.exe

git config --global difftool.bc3.path 'c:\Program Files (x86)\Beyond Compare 3\bcomp.exe'

and configure bc3 as default

git config --global diff.tool bc3
  Setting up KDiff3 as merge tool

The following should be added to your global .gitconfig file

[merge]
    tool = kdiff3
[mergetool "kdiff3"]
    path = D:/Program Files (x86)/KDiff3/kdiff3.exe
    keepBackup = false
    keepbackup = false
    trustExitCode = false

Remember to set the path property to point to the directory where you have installed KDiff3
  Setting up KDiff3 as diff tool 
[diff]
    tool = kdiff3
    guitool = kdiff3
[difftool "kdiff3"]
    path = D:/Program Files (x86)/KDiff3/kdiff3.exe
    cmd = \"D:/Program Files (x86)/KDiff3/kdiff3.exe\" \"$LOCAL\" \"$REMOTE\"
  Setting up an IntelliJ IDE as merge tool (Windows) 
[merge]
    tool = intellij
[mergetool "intellij"]
    cmd = cmd \"/C D:\\workspace\\tools\\symlink\\idea\\bin\\idea.bat merge $(cd $(dirname "$LOCAL") && pwd)/$(basename "$LOCAL") $(cd $(dirname "$REMOTE") && pwd)/$(basename "$REMOTE") $(cd $(dirname "$BASE") && pwd)/$(basename "$BASE") $(cd $(dirname "$MERGED") && pwd)/$(basename "$MERGED")\"
    keepBackup = false
    keepbackup = false
    trustExitCode = true

The one gotcha here is that this cmd property does not accept any weird characters in the path. If your IDE's install location has weird characters in it (e.g. it's installed in Program Files (x86), you'll have to create a symlink
  Setting up an IntelliJ IDE as diff tool (Windows) 
[diff]
    tool = intellij
    guitool = intellij
[difftool "intellij"]
    path = D:/Program Files (x86)/JetBrains/IntelliJ IDEA 2016.2/bin/idea.bat
    cmd = cmd \"/C D:\\workspace\\tools\\symlink\\idea\\bin\\idea.bat diff $(cd $(dirname "$LOCAL") && pwd)/$(basename "$LOCAL") $(cd $(dirname "$REMOTE") && pwd)/$(basename "$REMOTE")\"

The one gotcha here is that this cmd property does not accept any weird characters in the path. If your IDE's install location has weird characters in it (e.g. it's installed in Program Files (x86), you'll have to create a symlink

 

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