title: How to use backreferrence matches for simple math operations?
body: <p>I have one file looks like:</p>
  
  <pre><code>~ cat dump.txt
    &lt;ItemSpec id="46301" Day="1" Week="244251"/&gt;
    &lt;ItemSpec id="46302" Day="2" Week="244252"/&gt;
    &lt;ItemSpec id="46303" Day="3" Week="244253"/&gt;
    &lt;ItemSpec id="46304" Day="4" Week="244254"/&gt;
    &lt;ItemSpec id="46305" Day="5" Week="244255|244256|244257|244255|244256|244257|244255|244256|244257|244255|244256|244257"/&gt;
    ...
  </code></pre>
  
  <p>I want the <code>Week</code> column number add 100,000 after process, just like:</p>
  
  <pre><code>~ &lt;simple shell code&gt; dump.txt
    &lt;ItemSpec id="46301" Day="1" Week="344251"/&gt;
    &lt;ItemSpec id="46302" Day="2" Week="344252"/&gt;
    &lt;ItemSpec id="46303" Day="3" Week="344253"/&gt;
    &lt;ItemSpec id="46304" Day="4" Week="344254"/&gt;
    &lt;ItemSpec id="46305" Day="5" Week="344255|344256|344257|344255|344256|344257|344255|344256|344257|344255|344256|344257"/&gt;
    ...
  </code></pre>
  
  <p>I don't know if there is a simple way to use backreference as a number for math operation. And my helpless try as below:</p>
  
  <pre><code>~ awk '{print gensub(/([0-9]{6})/,"\\1+100000","g",$0)}' dump.txt
    &lt;ItemSpec id="46301" Day="1" Week="244251+100000"/&gt;
    &lt;ItemSpec id="46302" Day="2" Week="244252+100000"/&gt;
    &lt;ItemSpec id="46303" Day="3" Week="244253+100000"/&gt;
    &lt;ItemSpec id="46304" Day="4" Week="244254+100000"/&gt;
    &lt;ItemSpec id="46305" Day="5" Week="244255+100000|244256+100000|244257+100000|244255+100000|244256+100000|244257+100000|244255+100000|244256+100000|244257+100000|244255+100000|244256+100000|244257+100000"/&gt;
  
  
    ...
  </code></pre>
  
  <p>Any idea would be helpful, thank you!</p>