My git config

.gitconfig

[user]
	name = foo
	email = [email protected]
[push]
	default = simple
[core]
	editor = /opt/sublime_text/sublime_text %n
[color]
	ui = true
[alias]
	s = status
	c = checkout
	b = branch
	a = add
	lol = log --oneline --graph --decorate
[merge]
    tool = meld
    conflictstyle = diff3
[diff]
	tool = meld
[mergetool "meld"]
    trustExitCode = false
    cmd = meld $LOCAL $BASE $REMOTE --auto-merge --output $MERGED
[difftool "meld"]
	cmd = meld "$LOCAL" "$REMOTE"
[mergetool]
	keepBackup = false
[core]
	editor = vim

Git Configs

git config --global user.name "Thomas Lange"
git config --global user.email "[email protected]"

git config --global color.ui true
git config --global core.editor "vim"

git config --global alias.a add
git config --global alias.s status
git config --global alias.c checkout
git config --global alias.b branch
git config --global alias.lol 'log --oneline --graph --decorate'

git config --global merge.tool meld
git config --global mergetool.meld.cmd 'meld $LOCAL $BASE $REMOTE --auto-merge --output $MERGED'
git config --global mergetool.keepBackup false
git config --global mergetool.meld.trustExitCode false

git config --global diff.tool meld
git config --global difftool.meld.cmd 'meld $LOCAL $REMOTE'

meld.sh

#!/usr/bin/python

# use this for a simple symlink to /usr/local/bin/meld

import sys
import os
import subprocess
 
if len(sys.argv) > 1:
  left = os.path.abspath(sys.argv[1]);
else:
  left = ""
 
if len(sys.argv) > 2:
  right = os.path.abspath(sys.argv[2]);
else:
	right = ""
	mid = ""

if len(sys.argv) > 3:
  mid = right;
  right = os.path.abspath(sys.argv[3]);
else:
	right = ""
	mid = ""
 
MELDPATH = "/Applications/Meld.app"
arguments = " -n " + MELDPATH + " --args " + left + " " + mid + " " + right
 
p = subprocess.call(['open', '-W', '-a',  MELDPATH, '--args', left, mid, right])

OSX Old

[core]
	excludesfile = /Users/*****/.gitignore_global
[difftool "sourcetree"]
	cmd = opendiff \"$LOCAL\" \"$REMOTE\"
	path = 
[mergetool "sourcetree"]
	cmd = /Applications/SourceTree.app/Contents/Resources/opendiff-w.sh \"$LOCAL\" \"$REMOTE\" -ancestor \"$BASE\" -merge \"$MERGED\"
	trustExitCode = true
[user]
	name = *****
	email = ****
[push]
	default = simple
[diff]
	tool = 

Note Bene:
My git config --global does not like ' " sequences. SO it is better to directly edit the .gitconfig in $HOME
with the values:
[alias]
s = status
c = checkout
b = branch
a = add
lol = log --oneline --graph --decorate
[merge]
tool = meld
[diff]
tool = meld
[mergetool "meld"]
trustExitCode = false
cmd = meld "$BASE" "$LOCAL" "$REMOTE" "$MERGED"
[difftool "meld"]
cmd = meld "$LOCAL" "$REMOTE"

meld on oSX
Use this script to run: meld.sh
Link it to /usr/local/bin/meld