add script to get version number from a git branch (#53)

* add script to get version number from a git branch

* add examples

* format

* fix line ending

hack/scripts/get-version-from-branch.sh

@@ -0,0 +1,57 @@
+#!/usr/bin/env bash
+
+# This script will generate the version.
+#
+# First it verifies, that the current branch name is 'release-x.y',
+# where x and y are multi-digit integers.
+# It further looks into the existing tags, looking for ones that start with x.y.
+# If there is none, it will return x.y.0. Otherwise it will return x.y.z where z
+# is the highest existing value increase by one.
+#
+# Examples:
+# 1. The current git branch is 'release-1.0' and git has the tags '1.0.1', '1.0.2', 1.0.3':
+#    $ ./get-version-from-branch.sh
+#    1.0.4
+#
+# 2. The current branch is 'release-1.1' and git has no tags that start with '1.1':
+#    $ ./get-version-from-branch.sh
+#    1.0.0
+#
+# 3. The current branch is 'main':
+#    $ ./get-version-from-branch.sh
+#    Not on a release branch.
+#
+# Please note that this will exit with an error:
+#    ./get-version-from-branch.sh || echo "exit with error"
+#    Not on a release branch.
+#    exit with error
+#
+
+# Get the current branch name.
+current_branch=$(git rev-parse --abbrev-ref HEAD)
+
+# Check if the current branch is a release branch.
+if [[ $current_branch =~ ^release-([0-9]+)\.([0-9]+)$ ]]; then
+	# Extract x and y from the branch name. BASH_REMATCH is an array variable
+	# automatically generated by pattern matching ([[ ... ]]).
+	x=${BASH_REMATCH[1]}
+	y=${BASH_REMATCH[2]}
+
+	# Find the highest z value for the matching tags.
+	highest_z=$(git tag -l "$x.$y.*" | cut -d '.' -f 3 | sort -n | tail -n 1)
+
+	# Increment the highest z value by 1 or set to 0 if no matching tags are found.
+	if [ -z "$highest_z" ]; then
+		next_z=0
+	else
+		next_z=$((highest_z + 1))
+	fi
+
+	# Return the new version.
+	new_version="${x}.${y}.${next_z}"
+	echo "${new_version}"
+	exit 0
+else
+	echo "Not on a release branch."
+	exit 1
+fi