Created gist from http://www.hossainkhan.info/content/shell-script-backup-all-your-svn-repositories - see guideline and notes on the blog article.

svn-backup-cron.sh

#!/bin/sh
################################################
#
# Backup SVN repos to local folder
#
# @author   Hossain Khan
# @email    contact [at] hossainkhan [dot] info
# @version  v0.01
# @reldate  2010-03-27
################################################
#  Copyright (c) 2010 Hossain Khan
# 
# Permission is hereby granted, free of charge, to any person
# obtaining a copy of this software and associated documentation
# files (the "Software"), to deal in the Software without
# restriction, including without limitation the rights to use,
# copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the
# Software is furnished to do so, subject to the following
# conditions:
# 
# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.
# 
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
# OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
# HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
# WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
# FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
# OTHER DEALINGS IN THE SOFTWARE.
# ----------------------- END OF LICENSE TEXT ----------------------
 
# Record todays date
# --------------------
bakdate=$(date +%Y%m%d%H%M)
echo "--------------------------------"
echo "Running SVN backup $bakdate"
echo "--------------------------------\n"
 
# From where to backup repos?
# ---------------------------
svnrepos="/srv/svnrepos"
echo "\nGoing to backup all SVN repos located at: $svnrepos \n"
 
# Where to save the dump?
# ------------------------
bakdest="/home/username/SVN-BACKUPS"
 
# Location for USB drive? (to copy backup)
# ----------------------------------------
baktousb="/media/USB/Extra-BACKUP"
 
# _________NO-COFIG-REQUIRED-BELOW-THIS-LINE___________
 
# First go to SVN repo folder
cd $svnrepos
 
 
# Just make sure we have write access to backup-folder
if [ -d "$bakdest" ] && [ -w "$bakdest" ] ; then
  # Now $repo has folder names = project names
  for repo in *; do
    # do svn dump for each project
    echo "Taking backup/svndump for: $repo"
    echo "Executing : svnadmin dump $repo > $bakdest/$repo-$bakdate.svn.dump \n"
    # Now finally execute the backup
    svnadmin dump $repo > $bakdest/$repo-$bakdate.svn.dump
    # You can go an extra mile by applying tar-gz compression to svn-dumps
 
    # We also would like to save the dump to remote place/usb
    if [ -d "$baktousb" ] && [ -w "$baktousb" ] ; then
      # USB/other directory exists, copy the dump there
      echo "Going to copy $repo dump to $baktousb directory...\n"
      cp $bakdest/$repo-$bakdate.svn.dump $baktousb
    fi 
  done
else
  echo "Unable to continue SVN backup process."
  echo "$bakdest is *NOT* a directory or you do not have write permission."
fi
 
 
# End of backup script
echo "\n\n================================="
echo " - Backup Complete, THANK YOU :-]"