Add script to compute the number of authors per month

Author: kgryte

tools/git/scripts/authors_per_month

@@ -0,0 +1,32 @@
+#!/usr/bin/env bash
+#
+# Prints the number of authors per month.
+#
+# <weekday> <month> <year> <number_of_authors>
+
+# * `git log`
+#   - Show logs.
+# * `awk '{}'`
+#   - Compute number of authors per month.
+# * `sort -k1n -k2M`
+#   - Sort the year numerically and sort the second key as a month.
+# * `awk '{}'`
+#   - Format the output.
+git log --format=format:"%ad %aN" --date=format:"%b %Y" --use-mailmap | awk '
+{
+	mon = $1 OFS $2
+	name = $3 $4
+	key = mon SUBSEP name
+	if (key in lines) {
+		next
+	}
+	lines[mon,name] = 1
+	counts[mon] += 1
+}
+
+END {
+	for (mon in counts) {
+		print mon OFS counts[mon]
+	}
+}
+'  | sort -k2n -k1M