How to parse xml sibling element value with SED

Question

I have a xml file which contains following text:

<Cluster>
     <Name>CLS_20</Name>
     <JMXUserName>admin</JMXUserName>
     <JMXPassword>mypwd</JMXPassword>
</Cluster>
<Server>
    <Name>Server_20</Name>
    <IpAddress>a.b.c.d</IpAddress>
    <Port>1234</Port>
</Server>
<Server>
    <Name>Server_21</Name>
    <IpAddress>e.f.g.h</IpAddress>
    <Port>1234</Port>
</Server>

I have the IP address of the server (a.b.c.d) I want to retrieve name of the server (Server_20)

How can this be achieved with SED Or with any other linux command.

Please help.

Choose a language that has an XML parser. (Python, Perl, Ruby, etc). — chepner, Apr 17 '15 at 11:33

Wintermute · Answer 1 · 2015-04-17T12:36:25.637

Do not do this with sed; it will break horribly when benign formatting changes happen to the XML.

Use a proper XML-parsing tool. For example with xmlstarlet:

xmlstarlet sel -t -c '//Server[IpAddress="a.b.c.d"]/Name/node()' -n filename.xml

or with xmllint:

xmllint --xpath '//Server[IpAddress="a.b.c.d"]/Name/node()' filename.xml

or with old versions of xmllint that don't yet understand --xpath (if you are tempted to use this I encourage you to look at other tools):

echo 'cat //Server[IpAddress="a.b.c.d"]/Name/node()' | xmllint --shell filename.xml | sed '1d;$d'

or with the xpath utility from the XML::XPath Perl library:

xpath -q -e '//Server[IpAddress="a.b.c.d"]/Name/node()' filename.xml

...or with any of three dozen (dozen) other XML tools.

The heart of this is the XPath expression //Server[IpAddress="a.b.c.d"]/Name/node(). This consists of:

//Server refers to a Server node anywhere in the document
//Server/Name refers to a Name node that is the child of such a Server node
//Server/Name/node() refers to the contents of such a Name node
//Server[IpAddress="a.b.c.d"] refers to a server node that satisfies the condition IpAddress="a.b.c.d", which means that it has a child IpAddress node that contains a.b.c.d

Putting all that together, //Server[IpAddress="a.b.c.d"]/Name/node() refers to the contents of a Name node that is the child of a Server node anywhere in the document that has an IpAddress child node that contains a.b.c.d.

It is giving me unknown option --xpath when I am using xxllint : version is- xmllint: using libxml version 20706 — Sneha Patil, Apr 17 '15 at 12:08
That appears to be an old version of xmllint. Hum. Do you have any other XML-handling tools lying around? There are many that can filter for XPath expressions, so I'd rather look for a tool to use than hack something dirty together with `xmllint --shell` and grep. — Wintermute, Apr 17 '15 at 12:17
I can not use third party tools since its a customer machine. I am looking for simple and available way to parse that value within a script. — Sneha Patil, Apr 17 '15 at 12:30
Okay, then. I edited in a way to do it with old xmllint, but for the record: I don't consider it very pretty. Better than parsing XML with plain-text tools, but still. — Wintermute, Apr 17 '15 at 12:36

score 0 · Answer 2 · answered Apr 17 '15 at 11:55

Sed is to use with caution on xml due to lot of variation in structure but based on this sample

sed -n '
 /<Server>/ h
 /<Server>/,\#</Server># {
   H
   \#</Server># { 
      x
      s#.*<Name>\([^<]*\)<.*IpAddress>a.b.c.d<.*#\1#p
      }
   }' YourFile

Principle:

don't print unless explicitly asked
load section Server in buffer
when reaching end of section
- change the whole by keeping only name attribut if the ipadresse value is the same as a.b.c and in this case print the result

How to parse xml sibling element value with SED

2 Answers2