Bash function to build a changelog based on the tags and commit entries of a git repo

channgelog.sh

changelog_entry() {
    # Output individual changelog entry
    usage="changelog_entry <since> <until>"

    since=${1}
    until=${2}
    if [ "${since}" == "" ] ; then
        echo "No 'since' version"
        echo ${usage}
        return 1
    fi
    if [ "${until}" == "" ] ; then
        echo "No 'until' version"
        echo ${usage}
        return 1
    fi
    
    echo
    echo "## $until"
    echo
    git log "${since}...${until}" --pretty=format:"* %s" --reverse | grep -v Merge;
}

changelog() {
    # Output all commit entries for a git repo as a changelog
    until=''
    while read major; do
        # OSX `sort` does not support `--version-order` so first loop the
        # major part of the version number  
        while read since; do
            if [ "$until" != "" ]; then
                changelog_entry $since $until
            fi
            until=$since
        done < <(git tag | grep "^$major" | sort -r -t . -k 2 -n)
    done < <(git tag | sed -e 's/^\(v[^.]*\)\..*/\1/' | sort -u -r)
    # Find the first commit to output entries between the first commit and the
    # first tag.
    first=$(git rev-list --max-parents=0 HEAD)
    changelog_entry $first $until
}