Unity Git Hooks -> There are three files

pre-commit

#!/bin/bash
#
# An example hook script to verify what is about to be committed.
# Called by "git commit" with no arguments.  The hook should
# exit with non-zero status after issuing an appropriate message if
# it wants to stop the commit.
#
# To enable this hook, rename this file to "pre-commit".

ASSETS_DIR="$(git config --get unity3d.assets-dir || echo "Assets")"

if git rev-parse --verify HEAD >/dev/null 2>&1
then
	against=HEAD
else
	# Initial commit: diff against an empty tree object
	against=4b825dc642cb6eb9a060e54bf8d69288fbee4904
fi

# Redirect output to stderr.
exec 1>&2

git diff --cached --name-only --diff-filter=A -z $against -- "$ASSETS_DIR" | while read -d $'\0' f; do
	ext="${f##*.}"
	base="${f%.*}"

	if [ "$ext" = "meta" ]; then
		if [ $(git ls-files --cached -- "$base" | wc -l) = 0 ]; then
			cat <<EOF
Error: Redudant meta file.

Meta file \`$f' is added, but \`$base' is not in the git index.

Please add \`$base' to git as well.
EOF
			exit 1
		fi
	else
		p="$f"
		while [ "$p" != "$ASSETS_DIR" ]; do
			if [ $(git ls-files --cached -- "$p.meta" | wc -l) = 0 ]; then
				cat <<EOF
Error: Missing meta file.

Asset \`$f' is added, but \`$p.meta' is not in the git index.

Please add \`$p.meta' to git as well.
EOF
				exit 1
			fi
			p="${p%/*}"
		done
	fi
done

ret="$?"
if [ "$ret" != 0 ]; then
	exit "$ret"
fi

git diff --cached --name-only --diff-filter=D -z $against -- "$ASSETS_DIR" | while read -d $'\0' f; do
	ext="${f##*.}"
	base="${f%.*}"

	if [ "$ext" = "meta" ]; then
		if [ $(git ls-files --cached -- "$base" | wc -l) != 0 ]; then
			cat <<EOF
Error: Redudant meta file.

Meta file \`$f' is removed, but \`$base' is still in the git index.

Please remove \`$base' from git as well.
EOF
			exit 1
		fi
	else
		p="$f"
		while [ "$p" != "$ASSETS_DIR" ]; do
			if [ $(git ls-files --cached -- "$p" | wc -l) = 0 ] && [ $(git ls-files --cached -- "$p.meta" | wc -l) != 0 ]; then
				cat <<EOF
Error: Missing meta file.

Asset \`$f' is removed, but \`$p.meta' is still in the git index.

Please remove \`$p.meta' from git as well.
EOF
				exit 1
			fi
			p="${p%/*}"
		done
	fi
done

ret="$?"
if [ "$ret" != 0 ]; then
	exit "$ret"
fi