Updating value of xml tag through script

Question

I need to update the value of following xml tag through shell script.

<sample>4</sample>

I have tried with below, but it doesnt work..

sed -i '' 's/\(<[^"]*"sample">\)\([^<]*\)\(<[^>]*\)/\1"$sampleVal"\3/g' $CONFIG_FILE

Any idea what is missing?

Update with complete xml nodes:

<?xml version="1.0" encoding="ISO-8859-1"?>
     <Server>
     <userInput>
            <sample>0</sample>
            <A>
            <a1>9999</a1>
            <a2>11111</a2>
           </A>
           <B>
            <b1>10389</b1>
            <b2>8000</b2>
           </B>

         <C>10500</C>
         </userInput>
      </Server>

Update with namespace:

<?xml version="1.0" encoding="ISO-8859-1"?>
     <Server xmlns="http://a/b/c/sample.com">
     <userInput>
            <sample>0</sample>
            <A>
            <a1>9999</a1>
            <a2>11111</a2>
           </A>
           <B>
            <b1>10389</b1>
            <b2>8000</b2>
           </B>

         <C>10500</C>
         </userInput>
      </Server>

Answer 1

With xmlstarlet:

xmlstarlet ed -u '/Server/userInput/sample/text()' -v "100" file.xml

Output:

<?xml version="1.0"?>
<Server>
  <userInput>
    <sample>100</sample>
    <A>
      <a1>9999</a1>
      <a2>11111</a2>
    </A>
    <B>
      <b1>10389</b1>
      <b2>8000</b2>
    </B>
    <C>10500</C>
  </userInput>
</Server>

If you want to edit your file "in place" add option -L:

xmlstarlet ed -L -u '/Server/userInput/sample/text()' -v "100" file.xml

If you want to omit XML declaration (<?xml ...?>) add option -O:

xmlstarlet ed -O -u '/Server/userInput/sample/text()' -v "100" file.xml

Output:

<Server>
  <userInput>
    <sample>100</sample>
    <A>
      <a1>9999</a1>
      <a2>11111</a2>
    </A>
    <B>
      <b1>10389</b1>
      <b2>8000</b2>
    </B>
    <C>10500</C>
  </userInput>
</Server>