title: Sed get xml attribute value
body: <p>I have next xml file:</p>
  
  <pre><code>&lt;AutoTest&gt;
   &lt;Source&gt;EBS FX&lt;/Source&gt;
   &lt;CreateCFF&gt;No&lt;/CreateCFF&gt;
   &lt;FoXML descriptor="pb.fx.spotfwd.trade.feed" version="2.0"&gt;
     &lt;FxSpotFwdTradeFeed&gt;
       &lt;FxSpotFwd feed_datetime="17-Dec-2014 10:20:09" 
         cpty_sds_id="EBS" match_id="L845586141217" original_trade_id_feed="L80107141217" 
         value_date="20141218" trade_id_external="001-002141880445/5862" match_sds_id="EBSFeedCpty" 
         counter_ccy="USD" trade_id_feed="107" trade_type="S" feed_source_id="80"    quoting_term="M" 
         deal_ccy="GBP" rate="1.5" trade_date="20141217" modified_by="automation"    cpty_side="B" counter_amt="1500000"
         smart_match="0" booking_status_id="10" trade_status_id="22" deal_amt="1000000"  trade_direction="B"&gt;
         &lt;Notes /&gt;
       &lt;/FxSpotFwd&gt;
   &lt;/FxSpotFwdTradeFeed&gt;
   &lt;TestCases /&gt;
   &lt;/FoXML&gt;
  &lt;/AutoTest&gt;
  </code></pre>
  
  <p>How to get value of <strong>trade_id_external</strong> attribute by using sed?<br>
  I tried with this expression: <code>sed -n '/trade_id_external/s/.*=//p' ./file.xml</code>
  but no luck</p>