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Willem
Asked: 2015-02-21 05:09:03 +0800 CST

CLI command to update simple XML file

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I would like to programmatically update a string in a very simple XML config file, such as this:

<?xml version="1.0"?>
<x>
    <z>should be changed</z>
</x>
<y>
    <z>should NOT be changed</z>
</y>

Does a simple CLI command exist that will update x/z and NOT y/z ? Perhaps with an XPath selector argument, such as:

$ xml-update myfile.xml /x/z "my new string"

I could write something in Perl or Python, but given the simplicity of this problem, I guess there must be a clever Unix utility that does this already.

Update: I found this but it seems a bit overkill. And I would have to learn XSLT first. http://developerblog.redhat.com/2013/12/05/xml-editing-bash-script/

linux

1 Answers

  1. Best Answer

    You can use the xml2/2xml tools to process XML on the command line without too much fuss. xml2 converts an XML document into a line-oriented format suitable for use with traditional text processing tools like awk or sed, and 2xml takes this format and converts it back to XML.

    For your example, if I take this document:

    <?xml version="1.0"?>
<doc>
<x>
    <z>should be changed</z>
</x>
<y>
    <z>should NOT be changed</z>
</y>
</doc>

    Running xml2 on that content yields:

    $ xml2 < doc.xml
/doc/x/z=should be changed
/doc/y/z=should NOT be changed

    I can modify the content of the <z> element like this

    xml2 < doc.xml |
sed '/\/doc\/x\/z/ s/should be changed/look ma no hands/' |
2xml | tidyp -xml -i -q

    I'm using a sed search expression to look explicitly for the line starting with /doc/y/z, and then modifying the content of that line, which gives us:

    <doc>
  <x>
    <z>look ma no hands</z>
  </x>
  <y>
    <z>should NOT be changed</z>
  </y>
</doc>

    I passed the output through tidyp, an XML formatter, because otherwise the document would look like:

    <doc><x><z>look ma no hands</z></x><y><z>should NOT be changed</z></y></doc>

    ...which is syntactically correct but harder to read.

    • 4