libxo-csv - Man Page

The libxo library supports a "pluggable" encoder mechanism, and ships with an encoder for CSV (comma separated values) files. The encoder allows paths and fields to be selected out of the output contents:

  % df --libxo @csv
  name,total-blocks,used-blocks,available-blocks,used-percent,mounted-on
  zroot/ROOT/default,3825984331,29376725,3796607605,1,/
  devfs,1,1,0,100,/dev
  zroot/usr/home,3808301289,11693684,3796607605,0,/usr/home
  zroot/var/audit,3796607806,201,3796607605,0,/var/audit
  ...
  % df --libxo @csv+leafs=name.used-percent
  name,used-percent
  zroot/ROOT/default,1
  devfs,100
  zroot/usr/home,0
  zroot/var/audit,0
  ...
  % df --libxo @csv+leafs=available-blocks+no-header /
  3796607605

contains software to generate four "built-in" formats: text, XML, JSON, and HTML. These formats are common and useful, but there are other common and useful formats that users will want, and including them all in the libxo software would be difficult and cumbersome.

To allow support for additional encodings, libxo includes a "pluggable" extension mechanism for dynamically loading new encoders. libxo -based applications can automatically use any installed encoder.

Use the "encoder=XXX" option to access encoders. The following example uses the "cbor" encoder, saving the output into a file:

  df --libxo encoder=cbor > df-output.cbor

Encoders can support specific options that can be accessed by following the encoder name with a colon (':') or a plus sign ('+') and one of more options, separated by the same character:

  df --libxo encoder=csv+path=filesystem+leaf=name+no-header
  df --libxo encoder=csv:path=filesystem:leaf=name:no-header

These examples instructs libxo to load the "csv" encoder and pass the following options:

 path=filesystem
 leaf=name
 no-header

Each of these option is interpreted by the encoder, and all such options names and semantics are specific to the particular encoder. Refer to the intended encoder for documentation on its options.

The string "@" can be used in place of the string "encoder=".

  df --libxo @csv:no-header

libxo ships with a custom encoder for "CSV" files, a common format for comma separated values. The output of the CSV encoder can be loaded directly into spreadsheets or similar applications.

A standard for CSV files is provided in RFC 4180, but since the format predates that standard by decades, there are many minor differences in CSV file consumers and their expectations. The CSV encoder has a number of options to tailor output to those expectations.

Consider the following XML:

  % list-items --libxo xml,pretty
  <top>
    <data test="value">
      <item test2="value2">
        <sku test3="value3" key="key">GRO-000-415</sku>
        <name key="key">gum</name>
        <sold>1412</sold>
        <in-stock>54</in-stock>
        <on-order>10</on-order>
      </item>
      <item>
        <sku test3="value3" key="key">HRD-000-212</sku>
        <name key="key">rope</name>
        <sold>85</sold>
        <in-stock>4</in-stock>
        <on-order>2</on-order>
      </item>
      <item>
        <sku test3="value3" key="key">HRD-000-517</sku>
        <name key="key">ladder</name>
        <sold>0</sold>
        <in-stock>2</in-stock>
        <on-order>1</on-order>
      </item>
    </data>
  </top>

This output is a list of `instances` (named "item"), each containing a set of `leafs` ("sku", "name", etc).

The CSV encoder will emit the leaf values in this output as `fields` inside a CSV `record`, which is a line containing a set of comma-separated values:

  % list-items --libxo encoder=csv
  sku,name,sold,in-stock,on-order
  GRO-000-415,gum,1412,54,10
  HRD-000-212,rope,85,4,2
  HRD-000-517,ladder,0,2,1

Be aware that since the CSV encoder looks for data instances, when used with xo, the `--instance` option will be needed:

  % xo --libxo encoder=csv --instance foo 'The {:product} is {:status}0 stereo "in route"
  product,status
  stereo,in route

By default, the CSV encoder will attempt to emit any list instance generated by the application. In some cases, this may be unacceptable, and a specific list may be desired.

Use the "path" option to limit the processing of output to a specific hierarchy. The path should be one or more names of containers or lists.

For example, if the "list-items" application generates other lists, the user can give "path=top/data/item" as a path:

  % list-items --libxo encoder=csv:path=top/data/item
  sku,name,sold,in-stock,on-order
  GRO-000-415,gum,1412,54,10
  HRD-000-212,rope,85,4,2
  HRD-000-517,ladder,0,2,1

Paths are "relative", meaning they need not be a complete set of names to the list. This means that "path=item" may be sufficient for the above example.

The CSV encoding requires that all lines of output have the same number of fields with the same order. In contrast, XML and JSON allow any order (though libxo forces key leafs to appear before other leafs).

To maintain a consistent set of fields inside the CSV file, the same set of leafs must be selected from each list item. By default, the CSV encoder records the set of leafs that appear in the first list instance it processes, and extract only those leafs from future instances. If the first instance is missing a leaf that is desired by the consumer, the "leaf" option can be used to ensure that an empty value is recorded for instances that lack a particular leaf.

The "leafs" option can also be used to exclude leafs, limiting the output to only those leafs provided.

In addition, the order of the output fields follows the order in which the leafs are listed. "leafs=one.two" and "leafs=two.one" give distinct output.

So the "leafs" option can be used to expand, limit, and order the set of leafs.

The value of the leafs option should be one or more leaf names, separated by a period ("."):

  % list-items --libxo encoder=csv:leafs=sku.on-order
  sku,on-order
  GRO-000-415,10
  HRD-000-212,2
  HRD-000-517,1
  % list-items -libxo encoder=csv:leafs=on-order.sku
  on-order,sku
  10,GRO-000-415
  2,HRD-000-212
  1,HRD-000-517

Note that since libxo uses terminology from YANG (:RFC:`7950`), the data modeling language for NETCONF (:RFC:`6241`), which uses "leafs" as the plural form of "leaf". libxo follows that convention.

CSV files typical begin with a line that defines the fields included in that file, in an attempt to make the contents self-defining:

  sku,name,sold,in-stock,on-order
  GRO-000-415,gum,1412,54,10
  HRD-000-212,rope,85,4,2
  HRD-000-517,ladder,0,2,1

There is no reliable mechanism for determining whether this header line is included, so the consumer must make an assumption.

The csv encoder defaults to producing the header line, but the "no-header" option can be included to avoid the header line.

RFC 4180 specifies that fields containing spaces should be quoted, but many CSV consumers do not handle quotes. The "no-quotes" option instruct the CSV encoder to avoid the use of quotes.

RFC 4180 defines the end-of-line marker as a carriage return followed by a newline. This "CRLF" convention dates from the distant past, but its use was anchored in the 1980s by the `DOS` operating system.

The CSV encoder defaults to using the standard Unix end-of-line marker, a simple newline. Use the "dos" option to use the `CRLF` convention.

The handling of command-line options is complex, since there are three hierarchies in use, but the rules are:

• commas separate libxo options

    --libxo json,pretty,warn
      

• pluses separate encoder options

  --libxo @csv+dos+no-header,warn
      

• periods separate tag names

  --libxo @csv+leafs=name.used.free+dos,warn
      

libxo(3), xo_options(7)

The libxo library first appeared in FreeBSD 11.0. The CSV encoder first appeared in FreeBSD 13.0.

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

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

https://juniper.github.io/libxo/1.6.0/html/index.html

libxo lives on github as:

https://github.com/Juniper/libxo

The latest release of libxo is available at:

https://github.com/Juniper/libxo/releases

The libxo library was added in FreeBSD 11.0.

Phil Shafer