Ubuntu Manpage: xmlwf - Determines if an XML document is well-formed

NAME

       xmlwf - Determines if an XML document is well-formed

SYNOPSIS

       xmlwf [OPTIONS] [FILE ...]
       xmlwf -h | --help
       xmlwf -v | --version

DESCRIPTION

       xmlwf uses the Expat library to determine if an XML document is well-formed. It is non-validating.

       If  you  do  not specify any files on the command-line, and you have a recent version of xmlwf, the input
       file will be read from standard input.

WELL-FORMED DOCUMENTS

       A well-formed document must adhere to the following rules:

       • The file begins with an XML declaration. For instance, <?xml version="1.0"  standalone="yes"?>.   NOTE:
         xmlwf does not currently check for a valid XML declaration.

       • Every start tag is either empty (<tag/>) or has a corresponding end tag.

       • There  is  exactly one root element. This element must contain all other elements in the document. Only
         comments, white space, and processing instructions may come after the close of the root element.

       • All elements nest properly.

       • All attribute values are enclosed in quotes (either single or double).

       If the document has a DTD, and it strictly complies with that DTD, then the document is  also  considered
       valid.   xmlwf is a non-validating parser -- it does not check the DTD. However, it does support external
       entities (see the -x option).

OPTIONS

When an option includes an argument, you may specify the argument either separately ("-d output") or con‐
catenated with the option ("-doutput"). xmlwf supports both.

-a factor
Sets the maximum tolerated amplification factor for protection against amplification attacks like
the billion laughs attack (default: 100.0 for the sum of direct and indirect output and also for
allocations of dynamic memory). The amplification factor is calculated as ..

amplification := (direct + indirect) / direct

.. with regard to use of entities and ..

amplification := allocated / direct

.. with regard to dynamic memory while parsing. <direct> is the number of bytes read from the
primary document in parsing, <indirect> is the number of bytes added by expanding entities and
reading of external DTD files, combined, and <allocated> is the total number of bytes of dynamic
memory allocated (and not freed) per hierarchy of parsers.

NOTE: If you ever need to increase this value for non-attack payload, please file a bug report.

-b bytes
Sets the number of output bytes (including amplification) needed to activate protection against
amplification attacks like billion laughs (default: 8 MiB for the sum of direct and indirect out‐
put, and 64 MiB for allocations of dynamic memory). This can be thought of as an "activation
threshold".

NOTE: If you ever need to increase this value for non-attack payload, please file a bug report.

-c If the input file is well-formed and xmlwf doesn't encounter any errors, the input file is simply
copied to the output directory unchanged. This implies no namespaces (turns off -n) and requires
-d to specify an output directory.

-d output-dir
Specifies a directory to contain transformed representations of the input files. By default, -d
outputs a canonical representation (described below). You can select different output formats us‐
ing -c, -m and -N.

The output filenames will be exactly the same as the input filenames or "STDIN" if the input is
coming from standard input. Therefore, you must be careful that the output file does not go into
the same directory as the input file. Otherwise, xmlwf will delete the input file before it gener‐
ates the output file (just like running cat < file > file in most shells).

Two structurally equivalent XML documents have a byte-for-byte identical canonical XML representa‐
tion. Note that ignorable white space is considered significant and is treated equivalently to
data. More on canonical XML can be found at http://www.jclark.com/xml/canonxml.html .

-e encoding
Specifies the character encoding for the document, overriding any document encoding declaration.
xmlwf supports four built-in encodings: US-ASCII, UTF-8, UTF-16, and ISO-8859-1. Also see the -w
option.

-g bytes
Sets the buffer size to request per call pair to XML_GetBuffer and read (default: 8 KiB).

-h, --help
Prints short usage information on command xmlwf, and then exits. Similar to this man page but
more concise.

-k When processing multiple files, xmlwf by default halts after the the first file with an error.
This tells xmlwf to report the error but to keep processing. This can be useful, for example,
when testing a filter that converts many files to XML and you want to quickly find out which con‐
versions failed.

-m Outputs some strange sort of XML file that completely describes the input file, including charac‐
ter positions. Requires -d to specify an output file.

-n Turns on namespace processing. (describe namespaces) -c disables namespaces.

-N Adds a doctype and notation declarations to canonical XML output. This matches the example output
used by the formal XML test cases. Requires -d to specify an output file.

-p Tells xmlwf to process external DTDs and parameter entities.

Normally xmlwf never parses parameter entities. -p tells it to always parse them. -p implies -x.

-q Disable reparse deferral, and allow quadratic parse runtime on large tokens (default: reparse de‐
ferral enabled).

-r Normally xmlwf memory-maps the XML file before parsing; this can result in faster parsing on many
platforms. -r turns off memory-mapping and uses normal file IO calls instead. Of course, memory-
mapping is automatically turned off when reading from standard input.

Use of memory-mapping can cause some platforms to report substantially higher memory usage for
xmlwf, but this appears to be a matter of the operating system reporting memory in a strange way;
there is not a leak in xmlwf.

-s Prints an error if the document is not standalone. A document is standalone if it has no external
subset and no references to parameter entities.

-t Turns on timings. This tells Expat to parse the entire file, but not perform any processing. This
gives a fairly accurate idea of the raw speed of Expat itself without client overhead. -t turns
off most of the output options (-d, -m, -c, ...).

-v, --version
Prints the version of the Expat library being used, including some information on the compile-time
configuration of the library, and then exits.

-w Enables support for Windows code pages. Normally, xmlwf will throw an error if it runs across an
encoding that it is not equipped to handle itself. With -w, xmlwf will try to use a Windows code
page. See also -e.

-x Turns on parsing external entities.

Non-validating parsers are not required to resolve external entities, or even expand entities at
all. Expat always expands internal entities (?), but external entity parsing must be enabled ex‐
plicitly.

External entities are simply entities that obtain their data from outside the XML file currently
being parsed.

This is an example of an internal entity:

<!ENTITY vers '1.0.2'>

And here are some examples of external entities:

<!ENTITY header SYSTEM "header-&vers;.xml"> (parsed)
<!ENTITY logo SYSTEM "logo.png" PNG> (unparsed)

-- (Two hyphens.) Terminates the list of options. This is only needed if a filename starts with a
hyphen. For example:

xmlwf -- -myfile.xml

will run xmlwf on the file -myfile.xml.

Older versions of xmlwf do not support reading from standard input.

OUTPUT

       xmlwf outputs nothing for files which are problem-free.  If any input file is not well-formed, or if  the
       output for any input file cannot be opened, xmlwf prints a single line describing the problem to standard
       output.

       If  the  -k option is not provided, xmlwf halts upon encountering a well-formedness or output-file error.
       If -k is provided, xmlwf continues processing the remaining input files, describing problems  found  with
       any of them.

EXIT STATUS

       For  options  -v|--version or -h|--help, xmlwf always exits with status code 0. For other cases, the fol‐
       lowing exit status codes are returned:

       0      The input files are well-formed and the output (if requested) was written successfully.

       1      An internal error occurred.

       2      One or more input files were not well-formed or could not be parsed.

       3      If using the -d option, an error occurred opening an output file.

       4      There was a command-line argument error in how xmlwf was invoked.

BUGS

       The errors should go to standard error, not standard output.

       There should be a way to get -d to send its output to standard output rather than  forcing  the  user  to
       send it to a file.

       I  have  no  idea why anyone would want to use the -d, -c, and -m options. If someone could explain it to
       me, I'd like to add this information to this manpage.

AUTHOR

       This manual page was originally written by Scott Bronson <bronson@rinspin.com> in December 2001  for  the
       Debian  GNU/Linux  system  (but  may be used by others). Permission is granted to copy, distribute and/or
       modify this document under the terms of the GNU Free Documentation License, Version 1.1.

                                               September 24, 2025                                       XMLWF(1)