On page 163, the line
/usr/bin/svnlook log --transaction "$TXN" "$RPS" > /var/log/txn.log
should read
/usr/bin/svnlook log --transaction "$TXN" "$RPS" >> /var/log/txn.log
(Notice the > has been changed to a >>)
Many thanks to James Leinweber for noticing and reporting this error.