echo -e 'zero\none\ntwo\n\n    three'
zero
one
two

    three


##</code><code>##

echo -e 'zero\none\ntwo\n\n    three' | perl -0777 -pe 's{\s*(one\ntwo)\s*}{\n\n<begin block>\n\n$1\n\n<end block>\n\n}'
zero

<begin block>

one
two

<end block>

three


##</code><code>##

echo -e 'zero\none\ntwo\n\n    three' | perl -0777 -pe 's{\s*(one\ntwo)\s*?( *)}{\n\n<begin block>\n\n$1\n\n<end block>\n\n$2}'
zero

<begin block>

one
two

<end block>



    three