available-environment-variables()

Description

available-environment-variables() returns a sequence of strings, each being the name of an environment variable that the processor is willing to expose. The order of the returned sequence is implementation-defined. If the processor exposes no environment variables, the function returns the empty sequence.

This function is used as a companion to environment-variable(): first call available-environment-variables() to discover what is exposed, then call environment-variable() with a specific name to retrieve its value. This pattern avoids relying on the empty-sequence return from environment-variable() as the sole indicator of absence.

The set of available variables may differ between development and production environments. Processors may restrict exposure for security or sandboxing reasons.

Parameters

This function takes no parameters.

Return value

xs:string* — a sequence of environment variable names that the processor exposes, in implementation-defined order.

Examples

Listing available variables

Stylesheet:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="3.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output method="xml" indent="yes"/>

  <xsl:template match="/">
    <env-vars>
      <xsl:for-each select="sort(available-environment-variables())">
        <var name="{.}"/>
      </xsl:for-each>
    </env-vars>
  </xsl:template>
</xsl:stylesheet>

Output (varies by environment):

<env-vars>
  <var name="HOME"/>
  <var name="PATH"/>
  <var name="USER"/>
</env-vars>

Checking whether a specific variable is exposed

Stylesheet:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="3.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output method="text"/>

  <xsl:template match="/">
    <xsl:choose>
      <xsl:when test="'APP_MODE' = available-environment-variables()">
        Mode: <xsl:value-of select="environment-variable('APP_MODE')"/>
      </xsl:when>
      <xsl:otherwise>APP_MODE not available</xsl:otherwise>
    </xsl:choose>
  </xsl:template>
</xsl:stylesheet>

Output:

APP_MODE not available

Notes

• The result of available-environment-variables() may be an empty sequence even when the OS has environment variables set, if the processor has disabled access.
• The function is particularly useful in test harnesses that need to adapt behavior based on the current environment without hard-coding variable names.
• available-environment-variables() is a pure function: it has no side effects and returns the same result for repeated calls within a single transformation.
• In Saxon, this function returns all OS-level environment variables by default. Use Saxon’s -feature flag to restrict access if needed.

See also

• environment-variable()