# Parsing poorly written XML **URL:** \ **Category:** Ruby\ **Created:** [January 23, 2008, 11:35pm UTC](https://www.ruby-forum.com/t/parsing-poorly-written-xml/126989 "2008-01-23T23:35:10Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![cghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/898d66/32.png) [@cghost](https://www.ruby-forum.com/u/cghost)\ **Post date:** [January 23, 2008, 11:35pm UTC](https://www.ruby-forum.com/t/parsing-poorly-written-xml/126989/1 "2008-01-23T23:35:10Z")
I’ve found an application which dumps all the registry settings for installed applications into an .xml file for me (you can find it as “myuninstall” via google). I can’t figure out the ruby code I need from REXML to do the following: -find a particular “product\_name” in the xml file -if found, save off the “uninstall\_string” so I can execute it on the commandline and uninstall the app. I’m a newbie to Ruby, and I’m even newer to parsing XML with Ruby, so I’m struggling a bit. It seems there should be a way to navigate within that “item” after I match on the product name, but I can’t figure out how. Any guidance would be very VERY appreciated! Here’s a snippet of the problem xml: \ \ \Devicescape\ \DevicescapeDesktop\ 2.0.5 Devicescape DevicescapeDesktop No Yes \C:\Program Files\Devicescape\Devicescape\ \[http://www.devicescape.com/](http://www.devicescape.com/)\ \1/22/2008 4:42:14 PM\ \MsiExec.exe /I{C3BFE4FC-C9F6-494F-B3AB-ABD75556DDC5}\ \No\ \{C3BFE4FC-C9F6-494F-B3AB-ABD75556DDC5}\ Windows Installer \HKEY\_LOCAL\_MACHINE\ ---
**Author:** ![cghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/898d66/32.png) [@cghost](https://www.ruby-forum.com/u/cghost)\ **Post date:** [January 24, 2008, 12:20am UTC](https://www.ruby-forum.com/t/parsing-poorly-written-xml/126989/2 "2008-01-24T00:20:52Z")
On Jan 23, 4:07 pm, Phrogz [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > #=\> 42 > 17 > > > foo > 17 Or, using XPath more liberally (with the same DATA section as quoted above): require ‘rexml/document’ doc = REXML::Document.new( DATA.read ) p REXML::XPath.match( doc, “//item[name=‘foo’]/value/text()” ) #=\> [“42”, “17”] ---
**Author:** ![cghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/898d66/32.png) [@cghost](https://www.ruby-forum.com/u/cghost)\ **Post date:** [January 24, 2008, 12:10am UTC](https://www.ruby-forum.com/t/parsing-poorly-written-xml/126989/3 "2008-01-24T00:10:21Z")
On Jan 23, 3:35 pm, Patrick C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > I’ve found an application which dumps all the registry settings for > installed applications into an .xml file for me (you can find it as > “myuninstall” via google). > > I can’t figure out the ruby code I need from REXML to do the following: > -find a particular “product\_name” in the xml file > -if found, save off the “uninstall\_string” so I can execute it on the > commandline and uninstall the app. require ‘rexml/document’ doc = REXML::Document.new( DATA.read ) # Find ‘item’ elements at any level # that have a child ‘name’ element whose text value is ‘foo’ doc.each\_element( “//item[name=‘foo’]” ){ |item| # Find every child element of the item element # whose name is ‘value’, get the first one, and get its text puts item.get\_elements( “value” ).first.text } #=\> 42 #=\> 17 **END** foo 42 bar 17 foo 17 ---
**Author:** ![cghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/898d66/32.png) [@cghost](https://www.ruby-forum.com/u/cghost)\ **Post date:** [January 24, 2008, 1:08am UTC](https://www.ruby-forum.com/t/parsing-poorly-written-xml/126989/4 "2008-01-24T01:08:07Z")
Gavin K. wrote: > On Jan 23, 3:35 pm, Patrick C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > > I’ve found an application which dumps all the registry settings for > > installed applications into an .xml file for me (you can find it as > > “myuninstall” via google). > > > > I can’t figure out the ruby code I need from REXML to do the following: > > -find a particular “product\_name” in the xml file > > -if found, save off the “uninstall\_string” so I can execute it on the > > commandline and uninstall the app. > > require ‘rexml/document’ > doc = REXML::Document.new( DATA.read ) > > # Find ‘item’ elements at any level > > # that have a child ‘name’ element whose text value is ‘foo’ > > doc.each\_element( “//item[name=‘foo’]” ){ |item| > > # Find every child element of the item element > > # whose name is ‘value’, get the first one, and get its text > > puts item.get\_elements( “value” ).first.text > } > #=\> 42 > #=\> 17 > > **END** > > > foo > 42 > > > bar > 17 Wow! That worked on the first try! I knew there had to be a way, but I’m trying to whip this script out and I didn’t want to spend a week studying XML parsing options in Ruby to do it. You’ve saved me a bunch of effort. Now I just need to figure out how to gracefully bail out and continue on with the rest of the script if “foo” isn’t there at all. Uhm… I seem to be having trouble with that piece too. I’m sure it’s easier than the first problem, but maybe it’s just 'cause my brain is cooked right now… Thanks a bunch! ---
**Author:** ![cghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/898d66/32.png) [@cghost](https://www.ruby-forum.com/u/cghost)\ **Post date:** [January 24, 2008, 5:00am UTC](https://www.ruby-forum.com/t/parsing-poorly-written-xml/126989/5 "2008-01-24T05:00:59Z")
On Jan 23, 5:08 pm, Patrick C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Gavin K. wrote: > Wow! That worked on the first try! I knew there had to be a way, but > I’m trying to whip this script out and I didn’t want to spend a week > studying XML parsing options in Ruby to do it. You’ve saved me a bunch > of effort. Now I just need to figure out how to gracefully bail out > and continue on with the rest of the script if “foo” isn’t there at all. > Uhm… I seem to be having trouble with that piece too. I’m sure it’s > easier than the first problem, but maybe it’s just 'cause my brain is > cooked right now… The first piece of code I wrote has a potential to be cranky. doc.each\_element( “//item[name=‘foo’]” ){ |item| puts item.get\_elements( “value” ).first.text } If no …foo elements can be found, the block will never be called. However, if it finds such an element, but the doesn’t have a child, then item.get\_elements( “value” ) will return an empty array. Calling .first on an empty array will return nil, and then you’ll have an error when you try to run the ‘text’ method of nil. You could modify the above code to guard for this: doc.each\_element( “//item[name=‘foo’]” ){ |item| first\_value = item.get\_elements( “value” ).first if first\_value puts first\_value.text end } However, the second (single XPath query) solution I wrote is both shorter and also more fault tolerant. If you assume that there’s only one that will match the foo criterion, then you can change from REXML::XPath.match (which returns an array, possibly empty) to REXML::XPath.first (which returns either a single value, or nil). Something like: value = REXML::XPath.first( doc, “//item[name=‘foo’]/value/text()” ) if value # do my stuff here end Or, to use your exact case: # Returns the uninstall command run (if found), # or nil if the necessary info couldn’t be found. def uninstall\_product( xml\_string, prod\_name ) require ‘rexml’ include REXML uninstall\_command = XPath.first( Document.new( xml\_string ), “//item[product\_name=‘#{prod\_name}’]/uninstall\_string/text()” ) if uninstall\_command # Do the uninstall; maybe as simple as: `#{uninstall_command}` else warn "Either product ‘#{prod\_name}’ doesn’t exist, " + “or it doesn’t have an uninstall string.” end uninstall\_command end