Git diff.external script ... Handles multiple file diffs. Git will make tempory a file(s) when it is comparing from the repository.

git-meld.bash

#!/bin/bash
#  * expects meld to be on your default PATH
#
function detach_meld()
{
    local f1="/tmp/mld1-$(basename "$1")"
    local f2="/tmp/mld2-$(basename "$2")"
    
##  echo "f1 = ${f1}"
##  echo "f2 = ${f2}"

    cp "$1" "${f1}"
    cp "$2" "${f2}"
#
    (meld  --newtab  "${f1}" "${f2}" ; rm  "${f1}"  "${f2}" ) > /dev/null 2>&1  &    
}


detach_meld  "$2"  "$5"