move a git tag remotely using github API (avoiding any clone or fetch)

github-tag

#!/bin/sh
#
# moves a tag in a github repo
# 
# Usage: github-tag <tag-name> <ref> <apirepourl>
# 
# Examples:
#    github-tag env-staging heads/release https://usertoken@api.github.com/repos/user/reponame
#    github-tag env-production tags/env-staging https://usertoken@api.github.com/repos/user/reponame
if [ $# -lt 3 ]
then
    echo "usage: github-tag <tag-name> <ref> <apirepourl>
examples:
    github-tag env-staging heads/release https://usertoken@api.github.com/repos/user/reponame
    github-tag env-production tags/env-staging https://usertoken@api.github.com/repos/user/reponame"
    exit 1

fi

echo "moving tag $1"
current_sha=$(curl -fs $3/git/refs/tags/$1 | awk '/sha/ { print $2 }' | sed s/[^a-z0-9]//g)
if [ $? -ne 0 ]
then
    echo ' error getting tag $1'
    exit $?
fi
echo " from $current_sha"
sha=$(curl -fs $3/git/refs/$2 | awk '/sha/ { print $2 }' | sed s/[^a-z0-9]//g)
if [ $? -ne 0 ]
then
    echo ' error getting ref $2'
    exit $?
fi
echo " to $sha"
curl -fs -X PATCH -H "Content-Type: application/json" -d '{"sha":"'$sha'","force":"true"}' $3/git/refs/tags/$1
if [ $? -ne 0 ]
then
    echo ' error moving tag'
    exit $?
else
    echo ' done!'
fi