Symphony.

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

    <!--
        Get the extension of a filename

        Usage example:

        <xsl:call-template name="get-file-extension">
            <xsl:with-param name="path" select="my-upload/filename" />
        </xsl:call-template>
    -->

    <xsl:template name="get-file-extension">
        <xsl:param name="path"/>
        <xsl:choose>
            <xsl:when test="contains($path, '/')">
                <xsl:call-template name="get-file-extension">
                    <xsl:with-param name="path" select="substring-after($path, '/')"/>
                </xsl:call-template>
            </xsl:when>
            <xsl:when test="contains($path, '.')">
                <xsl:call-template name="get-file-extension">
                    <xsl:with-param name="path" select="substring-after($path, '.')"/>
                </xsl:call-template>
            </xsl:when>
            <xsl:otherwise>
                <xsl:value-of select="$path"/>
            </xsl:otherwise>
        </xsl:choose>
    </xsl:template>

</xsl:stylesheet>