xmllint:tldr:4a91c

The command xmllint --xpath "string(//${foo})" ${source_file-xml} is used to extract the value of an XML element that matches a specific XPath expression. Here's a breakdown of the command:

• xmllint: This is the name of the command-line tool used for parsing and manipulating XML files.
• --xpath "string(//${foo})": This option specifies the XPath expression to be executed. In this case, the expression is string(//${foo}). The ${foo} part is a variable placeholder, and the value of foo will be substituted at runtime.
  • //${foo}: This XPath expression selects all elements in the XML file that match the value of the foo variable. The // symbol means to search for elements anywhere in the document.
  • string(): This function converts the resulting XML element into a string value. It extracts the text content of the element.
• ${source_file-xml}: This specifies the input XML file from which the XPath expression will be executed. The ${source_file-xml} part is again a variable placeholder, and if the source_file variable is not set, it defaults to xml.

To summarize, the command will search for XML elements that match the value of the foo variable and extract the text content of those elements. The result will be printed to the console.