perl - 使用 perl XML::LibXML 解析

Question

我正在使用 perl 的 XML::LibXML 模块来解析来自设备的 XML 响应。
看来，我可以成功获取数据的唯一方法是修改来自设备的 XML 响应。
这是我从设备发出的 XML 响应:

<chassis-inventory xmlns="http://xml.juniper.net/junos/10.3D0/junos-chassis">

<chassis junosstyle="inventory">

<name>Chassis</name>

<serial-number>JN111863EAFF</serial-number>

<description>VJX1000</description>

<chassis-module>

<name>Midplane</name>

</chassis-module>

<chassis-module>

<name>System IO</name>

</chassis-module>

<chassis-module>

<name>Routing Engine</name>

<description>VJX1000</description>

<chassis-re-disk-module>

<name>ad0</name>

<disk-size>1953</disk-size>

<model>QEMU HARDDISK</model>

<serial-number>QM00001</serial-number>

<description>Hard Disk</description>

</chassis-re-disk-module>

</chassis-module>

<chassis-module>

<name>FPC 0</name>

<chassis-sub-module>

<name>PIC 0</name>

</chassis-sub-module>

</chassis-module>

<chassis-module>

<name>Power Supply 0</name>

</chassis-module>

</chassis>

</chassis-inventory>

这是我用来解析和查找序列号的 perl 代码，例如:

#!/bin/env perl
use strict;
use warnings;
use XML::LibXML;
my $f = ("/var/working/xmlstuff");
sub yeah {
my $ff;
my $f = shift;
open(my $fff,$f);
while(<$fff>) {
$_ =~ s/^\s+$//; 
$_ =~ s/^(<\S+)\s.*?=.*?((?:\/)?>)/$1$2/g;
$ff .= $_;
}
close($fff);
return $ff
}
my $tparse = XML::LibXML->new();
my $ss = $tparse->load_xml( string => &yeah($f));
print map $_->to_literal,$ss->findnodes('/chassis-inventory/chassis/serial-number');

如果我不使用正则表达式替换，则不会加载任何脚本来解析。
我可以理解换行符的去除，但是为什么我必须从 XML 响应中删除属性，所以它只在以下行时才有效:

<chassis-inventory xmlns="http://xml.juniper.net/junos/10.3D0/junos-chassis">

<chassis junosstyle="inventory">

变成这样:

<chassis-inventory>
<chassis>

这是 XML 响应还是 XML::LibXML 模块的问题？

有没有办法让它忽略文件中有空行而不使用正则表达式替换的事实？

谢谢您的帮助。

Answer 1

您的 XPATH 表达式失败的原因是 namespace ；你需要在上下文中搜索。这是来自 XML::libXML documentation 的解释:

NOTE ON NAMESPACES AND XPATH:

A common mistake about XPath is to assume that node tests consisting of an element name with no prefix match elements in the default namespace. This assumption is wrong - by XPath specification, such node tests can only match elements that are in no (i.e. null) namespace.

So, for example, one cannot match the root element of an XHTML document with $node->find('/html') since '/html' would only match if the root element had no namespace, but all XHTML elements belong to the namespace http://www.w3.org/1999/xhtml. (Note that xmlns="..." namespace declarations can also be specified in a DTD, which makes the situation even worse, since the XML document looks as if there was no default namespace).

为了解决这个问题，注册命名空间，然后使用命名空间搜索你的文档。这是一个适合您的示例:

#!/bin/env perl
use strict;
use warnings;
use XML::LibXML;

my $xml = XML::LibXML->load_xml( location => '/var/working/xmlstuff');
my $xpc = XML::LibXML::XPathContext->new($xml);
$xpc->registerNs('x', 'http://xml.juniper.net/junos/10.3D0/junos-chassis');

foreach my $node ($xpc->findnodes('/x:chassis-inventory/x:chassis/x:serial-number')) {

    print $node->textContent() . "\n";
}