xmlstarlet: Selecting element by it's position

问题:

I have this XML file

<?xml version="1.0" encoding="utf-8"?>
<xObject version="3.0" xmlns="http://schemas.microsoft.com/random/2006/objects">
    <section id="*" type="product">
        <table name="XFile">
            <row sourceLineNumber="D:\bla\bla\">
                <field>Borderish.fo</field>
                <field>Documents</field>
                <field>1</field>
                <field>This line here 1</field>
            </row>
            <row sourceLineNumber="D:\blah\blah\">
                <field>Charterish</field>
                <field>Documents</field>
                <field>1</field>
                <field>This line here 2</field>
            </row>
        </table>
    </section>
</xObject>

What I want to do is select every 4th element with xmlstarlet.

I managed to do this using XmlPad like this: //table[@name='XFile']/row/field[4]/text(), but unfortunately I must do this using xmlstarlet.

Also, if I delete the xObject's attributes/namespace, seems to work using the command: xml sel -t -v "//table/row/field[4]/text()" test.xml

Does anyone has any idea how this can be done? It's my first time trying to evaluate xpath.

Regards, Stefan

回答1:

You have to define a namespace and use it in your XPath expression:

$ xmlstarlet sel -N ns="http://schemas.microsoft.com/random/2006/objects" -t -v "//ns:table/ns:row/ns:field[4]/text()" test.xml

The command above uses -N ns="http://schemas.microsoft.com/random/2006/objects" to declare a namespace named ns that is set to the value of the default namespace in your XML file. Then the XPath expression is set so that this ns prefix is used.