Here is synopsis for 'xml val' command:

XMLStarlet Toolkit: Validate XML document(s)
Usage: xml val <options> [ <xml-file-or-uri> ... ]
where <options>
   -w or --well-formed        - validate well-formedness only (default)
   -d or --dtd <dtd-file>     - validate against DTD
   -s or --xsd <xsd-file>     - validate against XSD schema
   -r or --relaxng <rng-file> - validate against Relax-NG schema
   -e or --err                - print verbose error messages on stderr
   -b or --list-bad           - list only files which do not validate
   -g or --list-good          - list only files which validate
   -q or --quiet              - do not list files (return result code only)

NOTE: XML Schemas are not fully supported yet due to its incomplete
      support in libxml (see http://xmlsoft.org)

XMLStarlet is a command line toolkit to query/edit/check/transform
XML documents (for more information see http://xmlstar.sourceforge.net/)

EXAMPLE

# Validate XML document against DTD
xml val --dtd dtd/table.dtd xml/tab-obj.xml >/dev/null 2>&1; echo $?

Output:

1

EXAMPLE

# Validate against XSD schema
xml val -b -s xsd/table.xsd xml/table.xml xml/tab-obj.xml 2>/dev/null; echo $?

Output:

xml/tab-obj.xml
1