automatically generate version info from git HEAD

git-version.sh

@@ -0,0 +1,45 @@
+#!/bin/sh
+
+if ! git status; then
+	# Either it's not a git repository, or git is unavaliable.
+	# Just workaround.
+	echo "<!ENTITY version           \"unknown\">"         >  version.ent
+	echo "<!ENTITY versiond          \"unknown-systemd\">" >> version.ent
+	echo "<!ENTITY releasedate       \"unknown\">"         >> version.ent
+	echo "<!ENTITY copyrightdate     \"1999-2021\">"       >> version.ent
+	exit 0
+fi
+
+export LC_ALL=en_US.utf8
+export TZ=US/Pacific
+
+commit_date=$(git show -s --format=format:"%cd" --date=local)
+short_date=$(date --date "$commit_date" "+%Y%m%d")
+
+year=$(date --date "$commit_date" "+%Y")
+month=$(date --date "$commit_date" "+%B")
+month_digit=$(date --date "$commit_date" "+%m")
+day=$(date --date "$commit_date" "+%d")
+
+case $day in
+	"1" | "21" | "31" ) suffix="st";;
+	"2" | "22" ) suffix="nd";;
+	"3" | "23" ) suffix="rd";;
+	* ) suffix="th";;
+esac
+
+full_date="$month $day$suffix, $year"
+
+sha="g$(git describe --always)"
+version="GIT-$short_date-$sha"
+versiond="GIT-$short_date-$sha-systemd"
+
+if [ "$(git diff HEAD | wc -l)" != "0" ]; then
+	version="$version-MODIFIED"
+	versiond="$versiond-MODIFIED"
+fi
+
+echo "<!ENTITY version           \"$version\">"            >  version.ent
+echo "<!ENTITY versiond          \"$versiond\">"           >> version.ent
+echo "<!ENTITY releasedate       \"$full_date\">"          >> version.ent
+echo "<!ENTITY copyrightdate     \"1999-$year\">"          >> version.ent