How to execute XPath one-liners from shell?

📝 Tech Blog Post: How to Execute XPath One-Liners from Shell

Are you tired of manually sifting through XML files to find specific elements or attributes? 😫 Well, I have some good news for you! In this blog post, we will explore how to execute XPath one-liners from the shell using various command-line tools. 🚀

So, let's dive in!

The Quest for a Simple XPath Command-line Tool 🌟

A user on our tech forum recently asked if there was a package available for Ubuntu and CentOS that provides a command-line tool for executing XPath one-liners effortlessly. They specifically wanted a tool that could be easily installed and used without any additional wrappers or adaptations. 🤔

Here's an example of what they were looking for:

foo //element@attribute filename.xml

Tools That Come Close 🤏

Although there isn't an exact tool that meets all the requirements, let's explore some tools that come close:

1. Nokogiri 🖌️

Nokogiri is a Ruby gem that provides a simple and powerful way to parse and navigate XML and HTML documents. While it doesn't offer a standalone command-line tool, we can create a small Ruby wrapper to achieve our goal:

#!/usr/bin/ruby

require 'nokogiri'

Nokogiri::XML(STDIN).xpath(ARGV[0]).each do |row|
  puts row
end

You can use this wrapper by passing your XPath expression as a command-line argument. 🎉

2. XML::XPath 🐪

XML::XPath is a Perl module that allows you to perform XPath queries on XML documents. Similarly to Nokogiri, it doesn't provide a standalone tool, but we can create a Perl wrapper like this:

#!/usr/bin/perl

use strict;
use warnings;
use XML::XPath;

my $root = XML::XPath->new(ioref => 'STDIN');
for my $node ($root->find($ARGV[0])->get_nodelist) {
  print($node->getData, "\n");
}

Don't forget to make the wrapper executable using chmod +x <filename>.pl. With this wrapper, you can execute XPath queries from the command line. 💡

3. Limitations of Other Tools ❌

Although XML::XPath's xpath command can almost do the job, it still returns some noise in the output, such as <NODE> and attribute = "value". The xml_grep command from XML::Twig cannot handle expressions that don't return elements, so it cannot be used to extract attribute values directly.

An Alternative Solution 💡

Let's explore another solution that doesn't completely satisfy our initial question, but can be useful in certain scenarios. We have an XSLT stylesheet that can evaluate arbitrary XPath expressions. Here's a simplified version of it:

<?xml version="1.0"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0"
    xmlns:dyn="http://exslt.org/dynamic" extension-element-prefixes="dyn">
  <xsl:output omit-xml-declaration="yes" indent="no" method="text"/>
  <xsl:template match="/">
    <xsl:for-each select="dyn:evaluate($pattern)">
      <xsl:value-of select="dyn:evaluate($value)"/>
      <xsl:value-of select="'&#10;'"/>
    </xsl:for-each>
  </xsl:template>
</xsl:stylesheet>

We can run this XSLT stylesheet using the xsltproc command. Here's an example:

xsltproc --stringparam pattern //element/@attribute --stringparam value . arbitrary-xpath.xslt filename.xml

By modifying the pattern and value string parameters, you can evaluate arbitrary XPath expressions. 😎

Conclusion and Call-to-Action 📣

XPath one-liners can be quite powerful when executed directly from the command line. Although there isn't a perfect out-of-the-box solution that meets all requirements, we explored some tools that come close and an alternative approach using XSLT.

Now, it's your turn to give them a try. Share your experience in the comments below and let us know which tool or approach worked best for you. 💬

If you found this blog post helpful, be sure to share it with your fellow tech enthusiasts. Let's make XPath queries from the shell a breeze! 🌐