CODEWITHSUNDEEP
ruby
wani
wani

Reputation: 51

How to replace a particular line in xml with the new one in ruby

I have a requirement where I need to replace the element value with the new one and I dont want any other modification to be done to the file.

<mtn:test-case title='Power-Consist-Message'>
 <mtn:messages>
  <mtn:message sequence='4' correlation-key='0x0F04'>
  <mtn:header>
   <mtn:protocol-version>0x4</mtn:protocol-version>
   <mtn:message-type>0x0F04</mtn:message-type>
   <mtn:message-version>0x01</mtn:message-version>
   <mtn:gmt-time-switch>false</mtn:gmt-time-switch>
   <mtn:crc-calc-switch>1</mtn:crc-calc-switch>
   <mtn:encrypt-switch>false</mtn:encrypt-switch>
   <mtn:compress-switch>false</mtn:compress-switch>
   <mtn:ttl>999</mtn:ttl>
   <mtn:qos-class-of-service>0</mtn:qos-class-of-service>
   <mtn:qos-priority>2</mtn:qos-priority>
   <mtn:qos-network-preference>1</mtn:qos-network-preference>

this is how the xml file looks like, I want to replace 999 with "some other value", under s section, but when am doing that using formatter in ruby some other unwanted modifications are taking place, the code that am using is as belows

File.open(ENV['CadPath1']+ "conf\\cad-mtn-config.xml") do |config_file|
# Open the document and edit the file
config = Document.new(config_file)
    testField=config.root.elements[4].elements[11].elements[1].elements[1].elements[1].elements[11]
if testField.to_s.match(/<mtn:qos-network-preference>/)
   test=config.root.elements[4].elements[11].elements[1].elements[1].elements[1].elements[8].text="2"
# Write the result to a new file.
formatter = REXML::Formatters::Default.new
File.open(ENV['CadPath1']+ "conf\\cad-mtn-config.xml", 'w') do |result|
formatter.write(config, result)
end
end
end

when am writting the modifications to the new file, the xml file size is getting changed from 79kb to 78kb, is there any way to just replace the particular line in xml file and save changes without affecting the xml file. Please let me know soon...

Upvotes: 1

Views: 575

Answers (2)

DSimon
DSimon

Reputation: 3420

If you need to just literally replace that value without affecting anything else about the XML file, even if (as pointed by the Tin Man above) that would mean leaving the original XML file malformed, you can do that with direct string manipulation using a regular expression.

Assuming there is guaranteed to only be one <mtn:ttl> tag in your XML document, you could just do:

doc = IO.read("somefile.xml")
doc.sub! /<mtn:ttl>.+?<\/mtn:ttl>/, "<mtn:ttl>some other value<\/mtn:ttl>" 
File.open("somefile.xml", "w") {|fh| fh.write(doc)}

If there might be more than one <mtn:ttl> tag, then this is trickier; how much trickier depends on how you want to figure out which tag(s) to change.

Upvotes: 0

the Tin Man
the Tin Man

Reputation: 160551

I prefer Nokogiri as my XML/HTML parser of choice:

require 'nokogiri'

xml =<<EOT
<mtn:test-case title='Power-Consist-Message'>
 <mtn:messages>
  <mtn:message sequence='4' correlation-key='0x0F04'>
  <mtn:header>
   <mtn:protocol-version>0x4</mtn:protocol-version>
   <mtn:message-type>0x0F04</mtn:message-type>
   <mtn:message-version>0x01</mtn:message-version>
   <mtn:gmt-time-switch>false</mtn:gmt-time-switch>
   <mtn:crc-calc-switch>1</mtn:crc-calc-switch>
   <mtn:encrypt-switch>false</mtn:encrypt-switch>
   <mtn:compress-switch>false</mtn:compress-switch>
   <mtn:ttl>999</mtn:ttl>
   <mtn:qos-class-of-service>0</mtn:qos-class-of-service>
   <mtn:qos-priority>2</mtn:qos-priority>
   <mtn:qos-network-preference>1</mtn:qos-network-preference>
EOT

Notice that the XML is malformed, i.e., it doesn't terminate correctly.

doc = Nokogiri::XML(xml)

I'm using CSS accessors to find the ttl node. Because of some magic, Nokogiri's CSS ignores XML name spaces, simplifying finding nodes.

doc.at('ttl').content = '1000'
puts doc.to_xml


# >> <?xml version="1.0"?>
# >> <test-case title="Power-Consist-Message">
# >>  <messages>
# >>   <message sequence="4" correlation-key="0x0F04">
# >>   <header>
# >>    <protocol-version>0x4</protocol-version>
# >>    <message-type>0x0F04</message-type>
# >>    <message-version>0x01</message-version>
# >>    <gmt-time-switch>false</gmt-time-switch>
# >>    <crc-calc-switch>1</crc-calc-switch>
# >>    <encrypt-switch>false</encrypt-switch>
# >>    <compress-switch>false</compress-switch>
# >>    <ttl>1000</ttl>
# >>    <qos-class-of-service>0</qos-class-of-service>
# >>    <qos-priority>2</qos-priority>
# >>    <qos-network-preference>1</qos-network-preference>
# >> </header></message></messages></test-case>

Notice that Nokogiri replaced the content of the ttl node. It also stripped the XML namespace info because the document didn't declare it correctly, and, finally, Nokogiri has added closing tags to make the document syntactically correct.

If you want the namespace to be declared in the output, you'll need to make sure it's there in the input.

Upvotes: 2

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