xsl:variable

Description

xsl:variable binds a name to a computed value. Once the binding is established it cannot be changed — XSLT variables are constants in the sense that reassignment is not possible. This immutability is a fundamental design decision that enables the functional, side-effect-free processing model of XSLT.

A variable can be declared at two levels:

• Top-level (direct child of xsl:stylesheet): the variable is global and visible in all templates throughout the stylesheet and any included or importing stylesheets.
• Inside a template: the variable is local and visible only in the subsequent siblings and their descendants within the same template scope.

The value of a variable is determined either by the select attribute (an XPath expression) or by the element’s content. If neither is present, the variable has an empty string value. If both are present, it is an error.

Attributes

Examples

Local variable for intermediate computation

Input XML:

<?xml version="1.0" encoding="UTF-8"?>
<cart>
  <item price="12.50" qty="3">Widget</item>
  <item price="5.00" qty="10">Bolt</item>
</cart>

Stylesheet:

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

  <xsl:template match="/cart">
    <invoice>
      <xsl:apply-templates select="item"/>
    </invoice>
  </xsl:template>

  <xsl:template match="item">
    <xsl:variable name="subtotal" select="@price * @qty"/>
    <line>
      <name><xsl:value-of select="."/></name>
      <subtotal><xsl:value-of select="format-number($subtotal, '#0.00')"/></subtotal>
    </line>
  </xsl:template>
</xsl:stylesheet>

Output:

<invoice>
  <line><name>Widget</name><subtotal>37.50</subtotal></line>
  <line><name>Bolt</name><subtotal>50.00</subtotal></line>
</invoice>

Global variable and content-based variable

Input XML:

<?xml version="1.0" encoding="UTF-8"?>
<document><title>Annual Report</title><year>2025</year></document>

Stylesheet:

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

  <xsl:variable name="company">Acme Corp</xsl:variable>

  <xsl:template match="/document">
    <xsl:variable name="heading" select="concat(title, ' — ', $company, ' ', year)"/>
    <report>
      <heading><xsl:value-of select="$heading"/></heading>
    </report>
  </xsl:template>
</xsl:stylesheet>

Output:

<report>
  <heading>Annual Report — Acme Corp 2025</heading>
</report>

Notes

• A local xsl:variable does not shadow or override a global variable of the same name within the current scope; it creates a new binding that takes precedence locally.
• Because variables are immutable, the common pattern for conditional assignment is xsl:choose inside a content-based variable declaration.
• Circular variable references (a global variable referencing itself) are an error.
• In XSLT 1.0, a content-based variable that produces a result tree fragment (RTF) can only be used with string(), boolean(), number(), or passed to xsl:copy-of. To use it as a node-set, you need the node-set() extension function (e.g., exsl:node-set()).

See also

• xsl:param
• xsl:with-param