describe-version

#!/bin/bash

# constructs a version string from a Git repository according to the rules of Go modules
# https://golang.org/ref/mod#versions
# https://golang.org/ref/mod#pseudo-versions

shopt -s extglob

version="$(git tag --sort=-v:refname --points-at HEAD -l 'v*')" || exit 1
IFS=$'\n' read -r version <<< "$version"

case "$version" in
'');;
v+([0-9]).+([0-9]).+([0-9])?(-pre)?([+]*)) echo "${version:1}" && exit 0;;
*) exit 1;;
esac

version="$(git tag --sort=-v:refname --merged HEAD -l 'v*')" || exit 1
IFS=$'\n' read -r version <<< "$version"

case "$version" in
'') version="v0.0.0-";;
v+([0-9]).+([0-9]).+([0-9])-pre?([+]*)) version="${version%[+]*}" && version="$version.0.";;
v+([0-9]).+([0-9]).+([0-9])?([+]*)) version="${version%[+]*}" && version="${version%.*}.$((${version##*.} + 1))-";;
*) exit 1;;
esac

echo "${version:1}$(git show -s --date=format:"%Y%m%d%H%M%S" --format=%cd HEAD)-$(git rev-parse --short=12 HEAD)"