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first-of() Function (jcs and slax Namespaces)

Namespaces

http://xml.juniper.net/junos/commit-scripts/1.0http://xml.libslax.org/slax

SLAX Syntax

var $result = prefix:first-of(object, "expression");

XSLT Syntax

<xsl:variable name="result" select="prefix:first-of(object, 'expression')"/>

Release Information

Function introduced in Junos OS Release 7.6.

Support for the slax namespace http://xml.libslax.org/slax added in Junos OS Release 12.2.

Description

Return the first nonempty (non-null) item in a list. If all objects in the list are empty, the default expression is returned. This function provides the same functionality as an if / else-if / else construct but in a much more concise format.

The prefix associated with the namespace URI should be defined in the prefix-to-namespace mapping in the style sheet.

Parameters

expression
—

Default value returned if all objects in the list are empty.

object
—

List of objects.

Return Value

result
—

First nonempty (non-null) item in the object list. If all objects in the list are empty, the default expression is returned.

Usage Examples

In the following example, if the value of $a is empty, $b is checked. If the value of $b is empty, $c is checked. If the value of $c is empty, $d is checked. If the value of $d is empty, the string "none" is returned.

jcs:first-of($a, $b, $c, $d, "none")

In the following example, for each physical interface, the script checks for a description of each logical interface. If a logical interface description does not exist, the function returns the description of the (parent) physical interface. If the parent physical interface description does not exist, the function returns a message that no description was found.

var $rpc = <get-interface-information>;
var $results = jcs:invoke($rpc);
for-each ($results/physical-interface/logical-interface) {
    var $description = jcs:first-of(description, ../description, "no description found");
}

The equivalent XSLT code is:

<xsl:variable name="rpc">
   <get-interface-information/>
</xsl:variable>
<xsl:variable name="results" select="jcs:invoke($rpc)"/>
<xsl:for-each select="$results/physical-interface/logical-interface">
   <xsl:variable name="description"
        select="jcs:first-of(description, ../description, 'no description found')"/>
</xsl:for-each>

The code for the description variable declaration in the previous examples would be equivalent to the following more verbose if / else-if / else construct:

var $description = {
   if (description) {
      expr description;
   }
   else if (../description) {
      expr ../description; 
   }
   else {
      expr "no description found";
   }
}

See also Example: Displaying DNS Hostname Information Using an Op Script.

 

Related Documentation

 

Published: 2013-03-05

Download This Guide

Supported Platforms

 

Related Documentation

 

Published: 2013-03-05

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