text1.bash

#!/bin/bash -e

bin="${BASH_SOURCE[0]%.*}"

go build -o "$bin" "$bin.go"

for file in "$@"
do
    for rev in $(git log --format='format:%H' "$file" | head -n-1)
    do
        if ! diff <("$bin" <(git show "$rev:./$file") <(git show "$rev^:./$file")) <(git show "$rev:./$file") >&2
        then
            echo "$rev:./$file"
        fi
    done
done

text1.go

package main

import (
	"io"
	"io/ioutil"
	"os"
	"time"

	"github.com/sergi/go-diff/diffmatchpatch"
)

func readall(path string) string {
	file, _ := os.Open(path)
	text, _ := ioutil.ReadAll(file)
	return string(text)
}

func main() {
	text1 := readall(os.Args[1])
	text2 := readall(os.Args[2])
	dmp := diffmatchpatch.New()
	dmp.DiffTimeout = time.Hour
	// dmp.DiffTimeout = 0
	diffs := dmp.DiffMain(text1, text2, true)
	io.WriteString(os.Stdout, dmp.DiffText1(diffs))
}