
In brief, you can set a default mergetool by setting the user config variable merge.tool. Git mergetool is fully configurable so you can pretty much chose your favourite tool.
#Set p4merge as git mergetool but how to
$LOCALAPPDATA/Perforce/p4merge.exe), git does not seem to be expanding environment variables for paths (if you know how to get this working, please let me know or update this answer)

You can display list of supported tools by running: git mergetool -tool-help
#Set p4merge as git mergetool but full
note that by default Perforce will add its installation dir to PATH, thus no need to specify full path to p4merge in the commandĪs pointed out by Pakosz, latest msys git now "natively" supports p4merge (tested on 1.8.5.2.msysgit.0).added double quotes for all file names so that files with spaces can still be found by the merge tool (I tested this in msys Git from Powershell).the custom tool config value resides in "mergetool.cmd", not "merge.cmd" (silly me, spent an hour troubleshooting why git kept complaining about non-existing tool).valid for all git projects not just the current one The changes (relative to Charles Bailey): Or, from a windows cmd.exe shell, the second line becomes : git config -global "p4merge.exe \"$BASE\" \"$LOCAL\" \"$REMOTE\" \"$MERGED\""

To follow-up on Charles Bailey's answer, here's my git setup that's using p4merge (free cross-platform 3way merge tool) tested on msys Git (Windows) install: git config -global merge.tool p4merge
