XML parser and linter that supports XPath, a syntax for navigating XML trees.
# To return all nodes (tags) named "foo":
xmllint --xpath "//foo" source_file.xml
# To return the contents of the first node named "foo" as a string:
xmllint --xpath "string(//foo)" source_file.xml
# To return the href attribute of the second anchor element in an html file:
xmllint --html --xpath "string(//a[2]/@href)" webpage.xhtml
# To return human-readable (indented) XML from file:
xmllint --format source_file.xml
# To check that a XML file meets the requirements of its DOCTYPE declaration:
xmllint --valid source_file.xml
# To validate XML against DTD schema hosted online:
xmllint --dtdvalid URL source_file.xml