Help for this page
$ printf "Line1\nLine2\nLine3\n\nXYZ: Blah\n" | perl -p -e "$/=undef; +s|\nXYZ.+\n||" Line1 Line2 Line3
$ printf "Line1\nLine2\nLine3\n\nXYZ: Blah\n" | perl -n -e '$buf.=$_; +if ($buf=~s|\nXYZ.+\n||) {print $buf; $buf=""}' Line1 Line2 Line3