--- a/Makefile	Wed Dec 07 15:22:11 2016 -0800
+++ b/Makefile	Fri Dec 09 15:18:41 2016 +0100
@@ -8,15 +8,67 @@
 
 export CVS_RSH
 
-all: deploy
+CHECK_GEM := $(shell command -v gem 2> /dev/null)
+CHECK_JEKYLL := $(shell command -v jekyll 2> /dev/null)
+CHECK_JEKYLL_VERSION = $(shell jekyll --version | grep ^jekyll | sed 's/^.* //g')
 
-deploy: | $(SAVANNAH_DIR)
+deploy: | $(SAVANNAH_DIR) check_prerequisites
+	#
+	# Build static website into the subdirectory `_site` using Jekyll
+	#
 	jekyll build
+	#
+	# vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
+	# DANGAROUS STEP, ommitted by default.
+	#
+	# Remove all previous files in the target directory, but no directories at
+	# all or CVS related stuff.  This is due to a limitation of CVS, see
+	#
+	#   https://web.archive.org/web/20140629054602/http://ximbiot.com/cvs/manual/cvs-1.11.23/cvs_7.html#SEC69
+	#
+	# For some introduction to CVS, see https://savannah.nongnu.org/projects/cvs
+	# or http://www.cs.umb.edu/~srevilak/cvs.html.
+	#
+	# find $(SAVANNAH_DIR) -type f -not -path "*/CVS/*" -exec rm -f '{}' \;
+	#
+	# ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+	#
+	# Copy the content of that directory `_site` into the checked out
+	# Savannah CVS (see make target $(SAVANNAH_DIR)).
+	#
 	cp -a _site/. $(SAVANNAH_DIR)
+	#
+	# Add all potential new directories to CVS
+	#
 	cd $(SAVANNAH_DIR) && find . -type d -not -name "CVS" -exec cvs add '{}' \;
+	#
+	# Add all potential new files to CVS (the following command taken from
+	# http://stackoverflow.com/questions/5071/how-to-add-cvs-directories-recursively
+	# proved to be fast)
+	#
 	cd $(SAVANNAH_DIR) && find . -type f | grep -v CVS | xargs cvs add
+	#
+	# Commit the chages to get online.
+	#
 	cd $(SAVANNAH_DIR) && cvs commit
+	#
+	# Now everything should be visible to the world.
+	#
+
+check_prerequisites:
+ifndef CHECK_GEM
+	$(error "Command `gem` is not available please install rubygems")
+endif
+ifndef CHECK_JEKYLL
+	$(error "Command `jekyll` is not available. ${CHECK_JEKYLL_VERSION}  Try `gem install jekyll`")
+endif
+ifneq "3.3" "$(word 1, $(sort 3.3 $(CHECK_JEKYLL_VERSION)))"
+	$(error "Detected Jekyll version ${CHECK_JEKYLL_VERSION} (>= 3.3 required).")
+endif
+	@echo "All prerequisites fulfilled."
 
 $(SAVANNAH_DIR):
 	cd .. \
 	&& cvs -z3 -d:ext:$(USRNAME)@cvs.savannah.gnu.org:/web/octave checkout -P octave
+
+.DEFAULT_GOAL :=