Setup p4merge as a visual mergetool
$ git config --global merge.tool p4mergetool
$ git config --global mergetool.p4mergetool.cmd \
"/Applications/p4merge.app/Contents/Resources/launchp4merge \$PWD/\$BASE \$PWD/\$REMOTE \$PWD/\$LOCAL \$PWD/\$MERGED"
$ git config --global mergetool.p4mergetool.trustExitCode false
$ git config --global mergetool.keepBackup false
Setup p4merge as a visual diff tool
$ git config --global diff.tool p4mergetool
$ git config --global difftool.p4mergetool.cmd \
"/Applications/p4merge.app/Contents/Resources/launchp4merge \$LOCAL \$REMOTE"