unix - sed multiline remove before pattern -

hi have big log file trying xml data passed it.

i have big log file ressembles :

2016/01/01   bladh bqskjdqskldjqsdlqskdjqlskdj dazihzmkldjkdjqslkjd 2016/01/01:  qsdhqsdlkqsmdjqsldjqslkdjqlskdjqslkdjqslkdjqskdjqsd 2016/01/01: qsjdqmlskdmlqskdmcxxxx [qskjd][qsdjqslkdj] payload    :[<log><a>a</a> <b>b</b> <c>c</c> <id>xxxxx</id> <d>d</d> </log>]]  2016/01/01   bladh bqskjdqskldjqsdlqskdjqlskdj dazihzmkldjkdjqslkjd 2016/01/01:  qsdhqsdlkqsmdjqsldjqslkdjqlskdjqslkdjqslkdjqskdjqsd 2016/01/01: qsjdqmlskdmlqskdmcxxxx [qskjd][qsdjqslkdj] payload :[<log>    <a>a</a> <b>b</b> <c>c</c> <id>yyyyy</id> <d>d</d> </log>]] qskdmqlskdqlsdqlskdqlsdk qsdlkqsdlkqsdmlkqsdlk 

for using

  sed -n '/<start/{:start /\/end/!{n;b start};/xxxxx/p}' logfile 

and getting

    2016/01/01: qsjdqmlskdmlqskdmcxxxx [qskjd][qsdjqslkdj] payload    :[<log><a>a</a> <b>b</b> <c>c</c> <id>xxxxx</id> <d>d</d> </log>]] 

i retrieve whole xml , :

<log>        <a>a</a>    <b>b</b>    <c>c</c>    <id>xxxx</id>    <d>d</d> </log> 

thanks in advance

solution in txr:

@(repeat) @  (skip)payload :[<@tag>@preamble @  (collect) @middle @  (last) </@tag>]] @  (end) @  (output) <@tag>   @(trim-str preamble) @    (repeat)   @middle @    (end) </@tag> @  (end) @(end) 

run:

$ txr extract.txr data <log>   <a>a</a>   <b>b</b>   <c>c</c>   <id>xxxxx</id>   <d>d</d> </log> <log>   <a>a</a>   <b>b</b>   <c>c</c>   <id>yyyyy</id>   <d>d</d> </log>