Select node by its text value in xmlstarlet

Question

I am trying to extract the value of the 'Value' node, where the 'Key' node is 'state' within a bash shell:

<FrontendStatus xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="1.0" serializerVersion="1.1">
<script/>
 <State>
  <String>
   ...
   ...
  </String>
  <String>
   ...
   ...
  </String>
  <String>
   <Key>state</Key>
   <Value>WatchingLiveTV</Value>
  </String>
  <String>
   <Key>studiolevels</Key>
   <Value>1</Value>
  </String>
  <String>
   ...
   ...
  </String>
  <String>
   ...
   ...
  </String>
 </State>
</FrontendStatus>

I can extract the value if I reference the node directly:

$ xmlstarlet sel -t -m '/FrontendStatus[1]/State[1]/String[31]' -v Value <status.xml
WatchingLiveTV

But I would like to select it by the value of the 'Key' node instead

Answer 1

This XPath will select Value of a State based on its Key equalling state:

/FrontendStatus/State/String[Key='state']/Value

Or, in xmlstarlet:

$ xmlstarlet sel -t -m "/FrontendStatus/State/String[Key='state']" -v Value <status.xml

Will return WatchingLiveTV as requested.