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+====== A savvy space backup system for linux ======
+===== The idea =====
+Recently, in Linux Journal I came across with a backup system that really shocked me: the first time, it uses rsync to make a copy of all the data.
+The second day, it uses cp to create a copy of all the data by creating a new link to all the files that existed.
+After this, it uses rsync again: because rsync not delete the changed files, but unlink them, only the changed files were copied -and therefore consume disk space-.
+Conclusion: you have some copies of day-1, day-2, etc keeping only links to the files that have changed.
+===== Let's go for it =====
+<code bash>
+#!/bin/bash
+#
+# backup : a backup script who saves space using links when files doesn't change
+#
+#
+# configure source and destination
+# properly
+echo "CONFIGURATION PENDING"
+exit 0
+source=/home/xxx/tmp/10/source
+dest=/home/xxx/tmp/10/dest
+# safe settings
+umask 077
+PATH="/usr/bin:/bin:/sbin"
+# write a message (to a file, for screen, etc.)
+function msg
+{
+  echo $1
+} #msg
+function finish
+{
+  # remove possibly open files
+  echo 'Finished.'
+}
+function fail
+{
+  msg $0"Have to finish unexpectedly"
+  error_result=$?
+  finish
+}
+#
+# Here starts the program
+# -----------------------
+#
+msg "Trapping signals SIGHUP, SIGINT, SIGQUIT, SIGTERM"
+trap "fail" 1 2 3 15
+rm -rf  "$dest/07"
+mv "$dest/06" "$dest/07"
+mv "$dest/05" "$dest/06"
+mv "$dest/04" "$dest/05"
+mv "$dest/03" "$dest/04"
+mv "$dest/02" "$dest/03"
+mv "$dest/01" "$dest/02"
+# -a: preserves dates and times, permissions, etc.
+# -l: create hard links instead of copying
+cp -al "$dest/current" "$dest/01"
+rsync -avz --delete-after \
+           "$source/"  \
+           "$dest/current"
+finish
+</code>