set-version.sh

#!/bin/sh
script_name=`basename "$0"`
branch_name="$(git symbolic-ref HEAD 2>/dev/null)" ||
branch_name="(unnamed branch)"     # detached HEAD
branch_name=${branch_name##refs/heads/}

if [ -z "$1" ]
then
    echo "You must provide a version string, for instance:"
    echo "./$script_name v1.34.9-beta"
    exit
fi

if [ ! -e README.md ]
then
    echo "There is no README.md!"
    exit
fi

if grep -Fq "img.shields.io/badge/version" README.md
then
    
    echo "$1 in branch: $branch_name"
    echo $1 > version.txt
    version="${1//-/--}" # Badge URL need to escape hyphens as double hyphens
    
    sed -E "s:(badge\/version-)(.*)(-blue|-brightgreen|-green|-yellowgreen|-yellow|-orange|-red|-lightgrey):\1$version\3:g" README.md > README.tmp
    rm README.md
    mv README.tmp README.md
    
    git add README.md
    git add version.txt
    git commit -m "Update to version $1"
    git push origin $branch_name
    git tag -a $1 -m ''
    git push origin --tags
    echo "DONE!"
    
else
    # Badge URL not found
    echo "Badge code not found in README.md, you must add this:"
    echo "![version](https://img.shields.io/badge/version-X.X.3-blue)"
    exit
fi

Creates a version.txt file, updates READ.md badge and tags a new version.