XPath expression to get node based on attribute value

Question

I have the following input xml file:

<rootnode>
 <section id="1" status="fail">
  <outer status="fail">
   <inner status="fail"/>
   <inner status="pass"/>
  </outer>
  <outer status="pass">
   <inner status="pass"/>
  </outer>
  <outer status="pass"/>
  <outer status="fail"/>
 </section>
 <section id="2" status="fail">
  <outer status="fail">
   <inner status="pass"/>
   <inner status="fail"/>
   <inner status="inc"/>
  </outer>
 </section>
</rootnode>

I want to filter out all non-fail status nodes so that the result looks like this:

<rootnode>
 <section id="1" status="fail">
  <outer status="fail">
   <inner status="fail"/>
  </outer>
  <outer status="fail"/>
 </section>
 <section id="2" status="fail">
  <outer status="fail">
   <inner status="fail"/>
  </outer>
 </section>
</rootnode>

The <rootnode> must not necessarily be included in the result. I have tried to use xmllint with an xpath expression. I can extract specific nodes with

xmllint --xpath "//inner" input.xml
xmllint --xpath "//@status" input.xml

but they only either return the nodes without regard to the value of status or the only return the attribute without the surrounding nodes.

Is there a way to do this with an xpath expression? If not, a simple solution which incorporates other bash tools is fine, too.

Answer 1

Like @svasa said in a comment, you should use XSLT. You can easily process the XSLT in bash with xsltproc, xmlstarlet (using tr command), Saxon (java on the command line), etc.

Here's an example using xsltproc:

$ xsltproc so.xsl so.xml
<?xml version="1.0"?>
<rootnode>
  <section id="1" status="fail">
    <outer status="fail">
      <inner status="fail"/>
    </outer>
    <outer status="fail"/>
  </section>
  <section id="2" status="fail">
    <outer status="fail">
      <inner status="fail"/>
    </outer>
  </section>
</rootnode>

XML Input (so.xml)

<rootnode>
    <section id="1" status="fail">
        <outer status="fail">
            <inner status="fail"/>
            <inner status="pass"/>
        </outer>
        <outer status="pass">
            <inner status="pass"/>
        </outer>
        <outer status="pass"/>
        <outer status="fail"/>
    </section>
    <section id="2" status="fail">
        <outer status="fail">
            <inner status="pass"/>
            <inner status="fail"/>
            <inner status="inc"/>
        </outer>
    </section>
</rootnode>

XSLT 1.0 (so.xsl)

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output indent="yes"/>
  <xsl:strip-space elements="*"/>

  <xsl:template match="@*|node()">
    <xsl:copy>
      <xsl:apply-templates select="@*|node()"/>
    </xsl:copy>
  </xsl:template>

  <xsl:template match="*[@status[not(normalize-space()='fail')]]"/>

</xsl:stylesheet>

---

I have a small follow-up question, if you don't mind. When the input.xml file does not contain any status=fail nodes, then the output is just two lines: <?xml version="1.0"?> and <rootnode/>. Is it possible two suppress the output entirely in this case? It is not really a problem, I know how to work around it in bash. I am just interested if there is a clean solution via xslt.

What you could do is omit the XML declaration (omit-xml-declaration="yes" in xsl:output) and check to see if there are any elements with status="fail". I'd use a key (xsl:key) for this...

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output indent="yes" omit-xml-declaration="yes">
    <!--If you need to output the declaration when there
    are elements with status="fail", it might be best to post process files that
    only contain the xml declaration.-->
  </xsl:output>
  <xsl:strip-space elements="*"/>

  <!--Key of all elements with status="fail".-->  
  <xsl:key name="fails" match="*[@status='fail']" use="@status"/>

  <xsl:template match="/*[not(key('fails','fail'))]">
    <!--If there aren't any elements with status="fail", don't process
    anything else.-->
  </xsl:template>

  <xsl:template match="@*|node()">
    <xsl:copy>
      <xsl:apply-templates select="@*|node()"/>
    </xsl:copy>
  </xsl:template>

  <xsl:template match="*[@status[not(normalize-space()='fail')]]"/>

</xsl:stylesheet>