Git pre-receive hook

while read old_sha1 new_sha1 refname ; do
        echo "stdin: [$old_sha1] [$new_sha1] [$refname]"
        if [ "$old_sha1" == "0000000000000000000000000000000000000000" ] ; then
            commits=$new_sha1
        else
            commits=`git rev-list $old_sha1..$new_sha1`
        fi

    for commit in $commits
        do
            echo Commit is $commit
            echo "git describe --exact-match $commit 2>&1 | grep -o fatal | wc -w"
            tag=`git describe --exact-match $commit 2>&1 | grep -o fatal | wc -w`
            if [ $tag -eq 0 ]; then
                echo "As this is a tag, there's no need for any validation"
                exit 0
            fi
            echo Tag: $tag
        ...
        ...
        ...
        done
done