Bash Using Sed on a Variable

Question

I have an xml file which will always have the following block inside of it:

<Name NameType="Also Known As">
  <NameValue>
    <FirstName>name1</FirstName>
    <Surname>sur1</Surname>
  </NameValue>
  <NameValue>
    <FirstName>name2</FirstName>
    <Surname>sur2</Surname>
  </NameValue>
</Name>

There may be just one "NameValue" node inside this block or there may be many. My issue is that I only ever want to keep the first one and discard the rest. The example above would hence read:

<Name NameType="Also Known As">
  <NameValue>
    <FirstName>name1</FirstName>
    <Surname>sur1</Surname>
  </NameValue>
</Name>

I'd like to use sed for this purpose. I have written the above block to a variable and tried to manipulate that as follows:

var=$(sed -n '/<Name NameType="Also Known As">*/,/<\/Name>/p' $file)
sed -i 's/<\/NameValue>.*<\/Name>/<\/NameValue><\/Name>/g' "$var"

I get the following in return:

sed: can't read <Name NameType="Also Known As">...

I thought the above would have replaced everything between the first closing NameValue tag and the closing Name tag with nothing. I used the -i option as I want to save the changes to this file. Perhaps it's syntax related, or maybe my understanding of using the sed command on a variable is way off. A point to note is that these tags occur inside other nodes in the file and so doing one blanket update using sed would change blocks which i don't want to change. This is the reason I passed this block to a variable. Any pointer's in the right direction would be much appreciated.

Answer 1

As the previous comments point out, sed expects one or several input files (which may be something like stdin, of course). In your example code, you read the content of a file into a variable in a roundabout way, and then use that variable as the name of a file. That is bound to fail. While I'm sure you could achieve your objectives using sed , I do not advise it. Branching in sed is horrible. Use a more powerful tool, preferably xsltproc or something else that is designed to work with XML.

You could use a stylesheet similar to this:

<?xml version="1.0" encoding="ISO-8859-1"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:template match="/Name">
    <Name>
    <xsl:copy-of select="@*" />
    <xsl:copy-of select="*[1]" />
    </Name>
  </xsl:template>
</xsl:stylesheet>