git pre-push hook to unit test code before pushing to master branch

pre-push

#!/bin/sh

IFS=' '
z40=0000000000000000000000000000000000000000

while read local_ref local_sha remote_ref remote_sha
do
    remote_abbrev_ref=$(echo $remote_ref | cut -d/ -f3)
    if [ :$remote_abbrev_ref != :master ]; then
        exit 0
    fi

    if [ :local_sha = :z40 ]; then
        exit 0
    fi

    current_sha1=$(git rev-parse HEAD)

    echo local_sha $local_sha
    echo current_sha1 $current_sha1

    if [ :$local_sha != :$current_sha1 ]; then
        current_branch=$(git rev-parse --abbrev-ref HEAD)
        git checkout $local_sha
    fi

    npm test
    S=$?

    if [ :$local_sha != :$current_sha1 ]; then
        git checkout $current_branch
    fi
done

exit $S