xo - Man Page

emit formatted output based on format string and arguments

Examples (TL;DR)


xo[-options] [argument...]


The xo utility allows command line access to the functionality of the libxo library. Using xo, shell scripts can emit XML, JSON, or HTML using the same commands that emit text output.

--close path

Close tags for the given path

-C | --continuation

Indicates this output is a continuation of the previous output data and should appear on the same line. This is allows HTML output to be constructed correctly.

--depth num

Set the depth for pretty printing


Display help text

-H | --html

Generate HTML output

-J | --json

Generate JSON output

--leading-xpath path

Add a prefix to generated XPaths (HTML)


Indicate that this content is not the first in a series of sibling objects, which is vital information for "JSON" output, which requires a comma between such objects.

--open path

Open tags for the given path

-p | --pretty

Make 'pretty' output (add indent, newlines)

--style style

Generate given style (xml, json, text, html)

-T | --text

Generate text output (the default style)


Indicates the entire object should be placed inside a top-level object wrapper, specifically when generating JSON output.


Display version information

-W | --warn

Display warnings in text on stderr


Display warnings in xml on stdout

--wrap path

Wrap output in a set of containers

-X | --xml

Generate XML output


Add XPath data to HTML output

The xo utility accepts a format string suitable for xo_emit(3) and a set of zero or more arguments used to supply data for that string.

In addition, xo accepts any of the libxo options listed in xo_options(7).


In this example, xo is used to emit the same data encoded in text and then in XML by adding the "-p" (pretty) and "-X" (XML output) flags:

  % xo 'The {:product} is {:status}\n' stereo "in route"
  The stereo is in route
  % xo -p -X 'The {:product} is {:status}\n' stereo "in route"
  <status>in route</status>

In this example, the output from a xo command is shown in several styles:

  xo "The {k:name} weighs {:weight/%d} pounds.\n" fish 6

    The fish weighs 6 pounds.
    "name": "fish",
    "weight": 6
    <div class="line">
      <div class="text">The </div>
      <div class="data" data-tag="name">fish</div>
      <div class="text"> weighs </div>
      <div class="data" data-tag="weight">6</div>
      <div class="text"> pounds.</div>

The --wrap <path> option can be used to wrap emitted content in a specific hierarchy. The path is a set of hierarchical names separated by the '/' character.

  xo --wrap top/a/b/c '{:tag}' value

    "top": {
      "a": {
        "b": {
          "c": {
            "tag": "value"

The --open <path> and --close <path> can be used to emit hierarchical information without the matching close and open tag. This allows a shell script to emit open tags, data, and then close tags. The --depth option may be used to set the depth for indentation. The --leading-xpath may be used to prepend data to the XPath values used for HTML output style.

  xo --open top/data
  xo --depth 2 '{:tag}' value
  xo --close top/data

    "top": {
      "data": {
        "tag": "value"

See Also

libxo(3), xo_emit(3), xo_options(7)


The libxo library first appeared in FreeBSD 11.0.


libxo was written by Phil Shafer <phil@freebsd.org>.

Additional Documentation

FreeBSD uses libxo version 1.6.0. Complete documentation can be found on github:


libxo lives on github as:


The latest release of libxo is available at:



The libxo library was added in FreeBSD 11.0.


Phil Shafer

Referenced By


December 4, 2014