xmllint — command line XML tool
xmllint  [ --version  |   --debug  |   --shell  |   --xpath "  |   XPath_expression"--debugent  |   --copy  |   --recover  |   --noent  |   --noout  |   --nonet  |   --path "  |   PATH(S)"--load-trace  |   --htmlout  |   --nowrap  |   --valid  |   --postvalid  |   --dtdvalid   |   URL--dtdvalidfpi   |   FPI--timing  |   --output   |   FILE--repeat  |   --insert  |   --compress  |   --html  |   --xmlout  |   --push  |   --memory  |   --maxmem   |   NBBYTES--nowarning  |   --noblanks  |   --nocdata  |   --format  |   --encode   |   ENCODING--dropdtd  |   --nsclean  |   --testIO  |   --catalogs  |   --nocatalogs  |   --auto  |   --xinclude  |   --noxincludenode  |   --loaddtd  |   --dtdattr  |   --stream  |   --walker  |   --pattern   |   PATTERNVALUE--chkregister  |   --relaxng   |   SCHEMA--schema   |   SCHEMA--c14n ] { XML-FILE(S)...  |   - }
xmllint   --help 
		The xmllint program parses one or more XML files,
		specified on the command line as XML-FILE
		(or the standard input if the filename provided
		is - ). It prints various types of
		output, depending upon the options selected. It is useful for detecting
		errors both in XML code and in
		the XML parser itself.
	
xmllint is included in libxml(3).
xmllint accepts the following options (in alphabetical order):
--autoGenerate a small document for testing purposes.
--catalogs
			Use the SGML catalog(s) from SGML_CATALOG_FILES.
			Otherwise XML catalogs starting
			from /etc/xml/catalog are used by default.
		
--chkregisterTurn on node registration. Useful for developers testing libxml(3) node tracking code.
--compressTurn on gzip(1) compression of output.
--copyTest the internal copy implementation.
--c14n
			Use the W3C XML Canonicalisation (C14N) to
			serialize the result of parsing to stdout.
			It keeps comments in the result.
		
--dtdvalid URL
			Use the DTD specified by
			an URL for validation.
		
--dtdvalidfpi FPI
			Use the DTD specified by a Formal Public
			Identifier FPI for validation, note that this
			will require a catalog exporting that Formal Public Identifier to work.
		
--debugParse a file and output an annotated tree of the in-memory version of the document.
--debugentDebug the entities defined in the document.
--dropdtdRemove DTD from output.
--dtdattrFetch external DTD and populate the tree with inherited attributes.
--encode ENCODINGOutput in the given encoding. Note that this works for full document not fragments or result from XPath queries.
--format
			Reformat and reindent the output. The XMLLINT_INDENT
			environment variable controls the indentation. The default value is two
			spaces "  ").
		
--helpPrint out a short usage summary for xmllint.
--htmlUse the HTML parser.
--htmloutOutput results as an HTML file. This causes xmllint to output the necessary HTML tags surrounding the result tree output so the results can be displayed/viewed in a browser.
--insertTest for valid insertions.
--loaddtdFetch an external DTD.
--load-trace
			Display all the documents loaded during the processing
			to stderr.
		
--maxmem NNBYTES
			Test the parser memory support. NNBYTES
			is the maximum number of bytes the library is allowed to allocate.
			This can also be used to make sure batch processing
			of XML files will not exhaust the virtual memory
			of the server running them.
		
--memoryParse from memory.
--noblanksDrop ignorable blank spaces.
--nocatalogsDo not use any catalogs.
--nocdataSubstitute CDATA section by equivalent text nodes.
--noentSubstitute entity values for entity references. By default, xmllint leaves entity references in place.
--nonetDo not use the Internet to fetch DTDs or entities.
--nooutSuppress output. By default, xmllint outputs the result tree.
--nowarningDo not emit warnings from the parser and/or validator.
--nowrapDo not output HTML doc wrapper.
--noxincludenodeDo XInclude processing but do not generate XInclude start and end nodes.
--nscleanRemove redundant namespace declarations.
--output FILE
			Define a file path where xmllint will save the result of parsing.
			Usually the programs build a tree and save it
			on stdout, with this option
			the result XML instance will be saved onto a file.
		
--path "PATH(S)"
			Use the (space- or colon-separated) list of filesystem paths specified
			by PATHS to load DTDs or
			entities. Enclose space-separated lists by quotation marks.
		
--pattern PATTERNVALUEUsed to exercise the pattern recognition engine, which can be used with the reader interface to the parser. It allows to select some nodes in the document based on an XPath (subset) expression. Used for debugging.
--postvalidValidate after parsing has completed.
--pushUse the push mode of the parser.
--recoverOutput any parsable portions of an invalid document.
--relaxng SCHEMA
			Use RelaxNG file named SCHEMA
			for validation.
		
--repeatRepeat 100 times, for timing or profiling.
--schema SCHEMA
			Use a W3C XML Schema file
			named SCHEMA for validation.
		
--shellRun a navigating shell. Details on available commands in shell mode are below (see the section called “SHELL COMMANDS”).
--xpath "XPath_expression"Run an XPath expression given as argument and print the result. In case of a nodeset result, each node in the node set is serialized in full in the output. In case of an empty node set the "XPath set is empty" result will be shown and an error exit code will be returned.
--stream
			Use streaming API - useful when used in combination
			with --relaxng or --valid options
			for validation of files that are too large to be held in memory.
		
--testIOTest user input/output support.
--timingOutput information about the time it takes xmllint to perform the various steps.
--valid
			Determine if the document is a valid instance of the included
			Document Type Definition (DTD).
			A DTD to be validated against also can be
			specified at the command line using the --dtdvalid
			option. By default, xmllint also checks to determine if the
			document is well-formed.
		
--versionDisplay the version of libxml(3) used.
--walkerTest the walker module, which is a reader interface but for a document tree, instead of using the reader API on an unparsed document it works on an existing in-memory tree. Used for debugging.
--xincludeDo XInclude processing.
--xmlout
			Used in conjunction with --html. Usually
			when HTML is parsed the document is saved with
			the HTML serializer. But with this option the
			resulting document is saved with the XML
			serializer. This is primarily used to
			generate XHTML from HTML input.
		
		xmllint offers an interactive shell mode invoked with
		the --shell command. Available commands in shell mode
		include (in alphabetical order):
	
Display XML base of the node.
Leave the shell.
NODEDisplay the given node or the current one.
PATHChange the current node to the given path (if unique) or root if no argument is given.
PATHDumps information about the node (namespace, attributes, content).
PATHShow the structure of the subtree under the given path or the current node.
Leave the shell.
Show this help.
Display memory usage.
FILENAMELoad a new document with the given filename.
PATHList contents of the given path or the current directory.
Display the path to the current node.
Leave the shell.
FILENAMESave the current document to the given filename or to the original name.
validateCheck the document for errors.
FILENAMEWrite the current node to the given filename.
SGML_CATALOG_FILESSGML catalog behavior can be changed by redirecting
			queries to the user's own set of catalogs. This can be done by setting
			the SGML_CATALOG_FILES environment variable to a list
			of catalogs. An empty one should deactivate loading the
			default /etc/sgml/catalog catalog.
		
XML_CATALOG_FILESXML catalog behavior can be changed by redirecting
			queries to the user's own set of catalogs. This can be done by setting
			the XML_CATALOG_FILES environment variable to a space-separated
			list of catalogs. Use percent-encoding to escape spaces or other characters.
			An empty variable should deactivate loading the default /etc/xml/catalog catalog.
		
XML_DEBUG_CATALOGSetting the environment variable XML_DEBUG_CATALOG
			to non-zero using the export
			command outputs debugging information related to catalog operations.
		
XMLLINT_INDENTSetting the environment variable XMLLINT_INDENT
			controls the indentation. The default value is two spaces "  ".
		
xmllint return codes provide information that can be used when calling it from scripts.
No error
Unclassified
Error in DTD
Validation error
Validation error
Error in schema compilation
Error writing output
			Error in pattern (generated when --pattern option is used)
		
			Error in Reader registration (generated
			when --chkregister option is used)
		
Out of memory error
XPath evaluation error
libxml(3)
More information can be found at
libxml(3) web page https://gitlab.gnome.org/GNOME/libxml2