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This is an old revision of XPathExtension made by DavidLee on 2012-09-19 12:49:15.


XPath Extensions

With Version an XPath extension is available in xmlsh which allows calling into xmlsh from with any xpath context including xpath, xlst, xquery, and the builtin <[ ... ]> commands.

Note that in prior versions of xmlsh which used Saxon 9.2 or before, predeclaring the xmlsh namespace was required. This is no longer necessary (or works).

The namespace "xmlsh" is predeclared for the XML expression syntax <[ ... ]> as well as the xquery command.
For example, the following works without using an explicit declaration
echo <[  <foo/>/xmlsh:eval("xcat") ]>

Similary the syntax to xquery is supported
xquery -n -q 'xmls:eval("echo hi")'

In order to use the extension functions within the xpath, xquery or xslt commands it must be declared either within xmlsh or for the case of xquery and xslt within their code/stylesheets.

Extension functions implemented


The eval xpath function evaluates its first argument as an xmlsh string (identical to the eval command) and optionally its second argument as positional parameters. The return value of the eval function is the standard output of the command.

xecho <[ xmlsh:eval("xecho $*" , ("foo" , <bar/> , 1 )  )  ]>
xquery -n 'xmlsh:eval("xls")'
xpath -n 'xmlsh:eval("xls $*" , "*.xml")'
var=<[ xmlsh:eval("xls") ]>

Calling XSLT from XQuery.

An interesting use of eval is to call xslt from within xquery or visa-versa. The context is passed to eval as the stdin and the output of the command becomes the result value of the expression. These examples are in xquery either via the <[ ]> syntax or the xquery command and require calling xquery from xmlsh to activate the extension function.

Example, in an XQuery expression, or file run from xmlsh
/foo/bar/xmlsh:eval("xslt -f style.xsl")/spam

calls "xslt" with the sytlesheet "style.xsl" passing the input context from /foo/bar as the input and then the output is further evaluated to extract the /spam child

An alternative of the above which can use variables for the stylesheet
let $style := "style.xsl"
/foo/bar/xmlsh:eval("xslt" , ("-f" , $style) )/spam

An alternative which passes the input context as a third argument
let $style := "style.xsl"
xmlsh:eval("xslt" , ("-f" , $style), /foo/bar  )/spam

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