Modifying the attributes of an XML document using XSLT

Question

I have an XML file which has an @url attribute for the element <matimage> . Currently there is a certain image name in the @url attribute, say triangle.png . I want to apply XSLT and modify this URL so that it would be something like assets/images/triangle.png .

I tried the following XSLT:

<?xml version="1.0"?>
 <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
  <xsl:output method="xml" />

  <!-- Copy everything -->
  <xsl:template match="*">
    <xsl:copy>
     <xsl:copy-of select="@*" />
     <xsl:apply-templates />
   </xsl:copy>
  </xsl:template>

 <xsl:template match="@type[parent::matimage]">
   <xsl:attribute name="uri">
     <xsl:value-of select="NEW_VALUE"/>
   </xsl:attribute>
 </xsl:template>
</xsl:stylesheet>

As a first step I tried to replace the old value with a new value but that didn't seem to work. Please tell me how to prepend or append a new value to the existing value of the @url attribute.

Here is the sample XML:

   <material>
    <matimage url="triangle.png">
        Some text
    </matimage>
  </material>

Desired output:

   <material>
    <matimage url="assets/images/triangle.png">
        Some text
    </matimage>
  </material>

Answer 1

A solution for what you are trying to achieve could be:

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:output method="xml" indent="yes"/>

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

    <!-- Match all the attributes url within matimage elements -->
    <xsl:template match="matimage/@url">
        <xsl:attribute name="url">
            <!-- Use concat to prepend the value to the current value -->
            <xsl:value-of select="concat('assets/images/', .)" />
        </xsl:attribute>
    </xsl:template>

</xsl:stylesheet>