"git merge -s ours" vs "git merge -X ours"

#!/bin/sh

mkdir gittest
cd gittest
git init

git checkout master
echo "Line one" > bar
git add bar
git commit -m "Original commit"

git checkout -b fork1
echo "Line one and something" > bar
echo "Line two" > bam
git add bar bam
git commit -m "Fork1 commit."

git checkout master
git checkout -b fork2
echo "Line one and other stuff" > bar
echo "Line three" > baz
git add bar baz
git commit -m "Fork2 commit."

git checkout fork1
if [ "$1" = "ours" ]; then
  # `ls gittest` => bam bar
  # `cat gittest/bar` => Line one and something
  git merge -s ours fork2
else
  # `ls gittest` => bam bar baz
  # `cat gittest/bar` => Line one and something
  git merge -X ours fork2
fi