Question

I am trying to select values from an XML by XPath. I wonder whyxmlstarlet sel -t -m //data -v "." /tmp/test.xml does work and xmlstarlet sel -t -m //data /tmp/test.xml does not.

I know that option -v means view. However xmlstarlet sel -t -m //data -v /tmp/test.xml is getting stuck.

So, my question is how to use option view properly.

Answer 1

Actually, -v means value-of and -m means for-each. These refer to the XSLT definitions^*, since the sel subcommand simply generates an XSLT document and runs it on the input.

xmlstarlet sel -t -m //data /tmp/test.xml

This is a loop without a body, so there is no output.

xmlstarlet sel -t -m //data -v /tmp/test.xml

Here /tmp/test.xml is interpreted as the XPath expression to -v so this means: for-each data node, output the value-of nodes named test.xml beneath the tmp root node. And it expects the input XML to come from standard input so it will appear to be stuck.

You can always get the meaning of any sel command line as XSLT by using the -C option.

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* In recent versions of xmlstarlet (1.3+) -v will output the value-of each node in a nodelist separated by a newline, rather than the XSLT definition where value-of only outputs the string value of the first node.