<!---  PLEASE DO NOT EDIT DIRECTLY. EDIT THE .md.in FILE PLEASE. --->
<div>
<span class="quicklinks">
Quick links:
&nbsp;
<a class="quicklink" href="../reference-main-flag-list/index.html">Flags</a>
&nbsp;
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&nbsp;
<a class="quicklink" href="../reference-dsl-builtin-functions/index.html">Functions</a>
&nbsp;
<a class="quicklink" href="../glossary/index.html">Glossary</a>
&nbsp;
<a class="quicklink" href="../release-docs/index.html">Release docs</a>
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</div>
# File formats

Miller handles name-indexed data using several formats: some you probably know
by name, such as CSV, TSV, JSON, and JSON Lines -- and other formats you're likely already
seeing and using in your structured data.

Additionally, Miller gives you the option of including comments within your data.

## Examples

<pre class="pre-highlight-in-pair">
<b>mlr help file-formats</b>
</pre>
<pre class="pre-non-highlight-in-pair">
CSV/CSV-lite: comma-separated values with separate header line
TSV: same but with tabs in places of commas
+---------------------+
| apple,bat,cog       |
| 1,2,3               | Record 1: "apple":"1", "bat":"2", "cog":"3"
| 4,5,6               | Record 2: "apple":"4", "bat":"5", "cog":"6"
+---------------------+

JSON (array of objects):
+---------------------+
| [                   |
| {                   |
|  "apple": 1,        | Record 1: "apple":"1", "bat":"2", "cog":"3"
|  "bat": 2,          |
|  "cog": 3           |
| },                  |
| {                   |
|   "dish": {         | Record 2: "dish.egg":"7",
|     "egg": 7,       | "dish.flint":"8", "garlic":""
|     "flint": 8      |
|   },                |
|   "garlic": ""      |
| }                   |
| ]                   |
+---------------------+

JSON Lines (sequence of one-line objects):
+------------------------------------------------+
| {"apple": 1, "bat": 2, "cog": 3}               |
| {"dish": {"egg": 7, "flint": 8}, "garlic": ""} |
+------------------------------------------------+
  Record 1: "apple":"1", "bat":"2", "cog":"3"
  Record 2: "dish:egg":"7", "dish:flint":"8", "garlic":""

PPRINT: pretty-printed tabular
+---------------------+
| apple bat cog       |
| 1     2   3         | Record 1: "apple:"1", "bat":"2", "cog":"3"
| 4     5   6         | Record 2: "apple":"4", "bat":"5", "cog":"6"
+---------------------+

Markdown tabular (supported for output only):
+-----------------------+
| | apple | bat | cog | |
| | ---   | --- | --- | |
| | 1     | 2   | 3   | | Record 1: "apple:"1", "bat":"2", "cog":"3"
| | 4     | 5   | 6   | | Record 2: "apple":"4", "bat":"5", "cog":"6"
+-----------------------+

XTAB: pretty-printed transposed tabular
+---------------------+
| apple 1             | Record 1: "apple":"1", "bat":"2", "cog":"3"
| bat   2             |
| cog   3             |
|                     |
| dish 7              | Record 2: "dish":"7", "egg":"8"
| egg  8              |
+---------------------+

DKVP: delimited key-value pairs (Miller default format)
+---------------------+
| apple=1,bat=2,cog=3 | Record 1: "apple":"1", "bat":"2", "cog":"3"
| dish=7,egg=8,flint  | Record 2: "dish":"7", "egg":"8", "3":"flint"
+---------------------+

NIDX: implicitly numerically indexed (Unix-toolkit style)
+---------------------+
| the quick brown     | Record 1: "1":"the", "2":"quick", "3":"brown"
| fox jumped          | Record 2: "1":"fox", "2":"jumped"
+---------------------+
</pre>

## CSV/TSV/ASV/USV/etc.

When `mlr` is invoked with the `--csv` or `--csvlite` option, key names are found on the first record and values are taken from subsequent records.  This includes the case of CSV-formatted files.  See [Record Heterogeneity](record-heterogeneity.md) for how Miller handles changes of field names within a single data stream.

Miller has record separator `RS` and field separator `FS`, just as `awk` does. (See also the [separators page](reference-main-separators.md).)

**TSV (tab-separated values):** `FS` is tab and `RS` is newline (or carriage return + linefeed for
Windows).  On input, if fields have `\r`, `\n`, `\t`, or `\\`, those are decoded as carriage return,
newline, tab, and backslash, respectively. On output, the reverse is done -- for example, if a field
has an embedded newline, that newline is replaced by `\n`.

**ASV (ASCII-separated values):** the flags `--asv`, `--iasv`, `--oasv`, `--asvlite`, `--iasvlite`, and `--oasvlite` are analogous except they use ASCII FS and RS `0x1f` and `0x1e`, respectively.

**USV (Unicode-separated values):** likewise, the flags `--usv`, `--iusv`, `--ousv`, `--usvlite`, `--iusvlite`, and `--ousvlite` use Unicode FS and RS `U+241F` (UTF-8 `0x0xe2909f`) and `U+241E` (UTF-8 `0xe2909e`), respectively.

Miller's `--csv` flag supports [RFC-4180 CSV](https://tools.ietf.org/html/rfc4180). This includes CRLF line-terminators by default, regardless of platform.

Here are the differences between CSV and CSV-lite:

* CSV-lite naively splits lines on newline, and fields on comma -- embedded commas and newlines are not escaped in any way.

* CSV supports [RFC-4180](https://tools.ietf.org/html/rfc4180)-style double-quoting, including the ability to have commas and/or LF/CRLF line-endings contained within an input field; CSV-lite does not.

* CSV does not allow heterogeneous data; CSV-lite does (see also [Record Heterogeneity](record-heterogeneity.md)).

* TSV-lite is simply CSV-lite with field separator set to tab instead of comma.
In particular, no encode/decode of  `\r`, `\n`, `\t`, or `\\` is done.

* CSV-lite allows changing FS and/or RS to any values, perhaps multi-character.

* In short, use-cases for CSV-lite and TSV-lite are often found when dealing with CSV/TSV files which are formatted in some non-standard way -- you have a little more flexibility available to you. (As an example of this flexibility: ASV and USV are nothing more than CSV-lite with different values for FS and RS.)

CSV, TSV, CSV-lite, and TSV-lite have in common the `--implicit-csv-header` flag for input and the `--headerless-csv-output` flag for output.

See also the [`--lazy-quotes` flag](reference-main-flag-list.md#csv-only-flags) which can help with CSV files which are not fully compliant with RFC-4180.

## JSON

[JSON](https://json.org) is a format which supports scalars (numbers, strings,
boolean, etc.) as well as "objects" (maps) and "arrays" (lists), while Miller
is a tool for handling **tabular data** only.  By *tabular JSON* I mean the
data is either a sequence of one or more objects, or an array consisting of one
or more objects.  Miller treats JSON objects as name-indexed records.

This means Miller cannot (and should not) handle arbitrary JSON.  In practice,
though, Miller can handle single JSON objects as well as list of them. The only
kinds of JSON that are unmillerable are single scalars (e.g. file contents `3`)
and arrays of non-object (e.g. file contents `[1,2,3,4,5]`).  Check out
[jq](https://stedolan.github.io/jq/) for a tool which handles all valid JSON.

In short, if you have tabular data represented in JSON -- lists of objects,
either with or without outermost `[...]` -- [then Miller can handle that for
you.

### Single-level JSON objects

An **array of single-level objects** is, quite simply, **a table**:

<pre class="pre-highlight-in-pair">
<b>mlr --json head -n 2 then cut -f color,shape data/json-example-1.json</b>
</pre>
<pre class="pre-non-highlight-in-pair">
[
{
  "color": "yellow",
  "shape": "triangle"
},
{
  "color": "red",
  "shape": "square"
}
]
</pre>

<pre class="pre-highlight-in-pair">
<b>mlr --json head -n 2 then cut -f color,u,v data/json-example-1.json</b>
</pre>
<pre class="pre-non-highlight-in-pair">
[
{
  "color": "yellow",
  "u": 0.632170,
  "v": 0.988721
},
{
  "color": "red",
  "u": 0.219668,
  "v": 0.001257
}
]
</pre>

Single-level JSON data goes back and forth between JSON and tabular formats
in the direct way:

<pre class="pre-highlight-in-pair">
<b>mlr --ijson --opprint head -n 2 then cut -f color,u,v data/json-example-1.json</b>
</pre>
<pre class="pre-non-highlight-in-pair">
color  u        v
yellow 0.632170 0.988721
red    0.219668 0.001257
</pre>

<pre class="pre-highlight-in-pair">
<b>mlr --ijson --opprint cat data/json-example-1.json</b>
</pre>
<pre class="pre-non-highlight-in-pair">
color  shape    flag i  u        v        w        x
yellow triangle 1    11 0.632170 0.988721 0.436498 5.798188
red    square   1    15 0.219668 0.001257 0.792778 2.944117
red    circle   1    16 0.209017 0.290052 0.138103 5.065034
red    square   0    48 0.956274 0.746720 0.775542 7.117831
purple triangle 0    51 0.435535 0.859129 0.812290 5.753095
red    square   0    64 0.201551 0.953110 0.771991 5.612050
purple triangle 0    65 0.684281 0.582372 0.801405 5.805148
yellow circle   1    73 0.603365 0.423708 0.639785 7.006414
yellow circle   1    87 0.285656 0.833516 0.635058 6.350036
purple square   0    91 0.259926 0.824322 0.723735 6.854221
</pre>

### Nested JSON objects

Additionally, Miller can **tabularize nested objects by concatenating keys**. If your processing has
input as well as output in JSON format, JSON structure is preserved throughout the processing:

<pre class="pre-highlight-in-pair">
<b>mlr --json head -n 2 data/json-example-2.json</b>
</pre>
<pre class="pre-non-highlight-in-pair">
[
{
  "flag": 1,
  "i": 11,
  "attributes": {
    "color": "yellow",
    "shape": "triangle"
  },
  "values": {
    "u": 0.632170,
    "v": 0.988721,
    "w": 0.436498,
    "x": 5.798188
  }
},
{
  "flag": 1,
  "i": 15,
  "attributes": {
    "color": "red",
    "shape": "square"
  },
  "values": {
    "u": 0.219668,
    "v": 0.001257,
    "w": 0.792778,
    "x": 2.944117
  }
}
]
</pre>

But if the input format is JSON and the output format is not (or vice versa) then key-concatenation applies:

<pre class="pre-highlight-in-pair">
<b>mlr --ijson --opprint head -n 4 data/json-example-2.json</b>
</pre>
<pre class="pre-non-highlight-in-pair">
flag i  attributes.color attributes.shape values.u values.v values.w values.x
1    11 yellow           triangle         0.632170 0.988721 0.436498 5.798188
1    15 red              square           0.219668 0.001257 0.792778 2.944117
1    16 red              circle           0.209017 0.290052 0.138103 5.065034
0    48 red              square           0.956274 0.746720 0.775542 7.117831
</pre>

This is discussed in more detail on the page [Flatten/unflatten: JSON vs. tabular formats](flatten-unflatten.md).

Use `--jflatsep yourseparatorhere` to specify the string used for key concatenation: this defaults to a single dot.

### JSON-in-CSV

It's quite common to have CSV data which contains stringified JSON as a column.
See the [JSON parse and stringify section](reference-main-data-types.md#json-parse-and-stringify) for ways to
decode these in Miller.

## JSON Lines

[JSON Lines](https://jsonlines.org) is similar to JSON, except:

* UTF-8 encoding must be supported
* There is no outermost `[...]`
* Each record is on a single line

Miller handles this:

<pre class="pre-highlight-in-pair">
<b>mlr --icsv --ojson head -n 2 example.csv</b>
</pre>
<pre class="pre-non-highlight-in-pair">
[
{
  "color": "yellow",
  "shape": "triangle",
  "flag": "true",
  "k": 1,
  "index": 11,
  "quantity": 43.6498,
  "rate": 9.8870
},
{
  "color": "red",
  "shape": "square",
  "flag": "true",
  "k": 2,
  "index": 15,
  "quantity": 79.2778,
  "rate": 0.0130
}
]
</pre>

<pre class="pre-highlight-in-pair">
<b>mlr --icsv --ojsonl head -n 2 example.csv</b>
</pre>
<pre class="pre-non-highlight-in-pair">
{"color": "yellow", "shape": "triangle", "flag": "true", "k": 1, "index": 11, "quantity": 43.6498, "rate": 9.8870}
{"color": "red", "shape": "square", "flag": "true", "k": 2, "index": 15, "quantity": 79.2778, "rate": 0.0130}
</pre>

Note that for _input_ data, either is acceptable: whether you use `--ijson` or `--ijsonl`, Miller
won't reject your input data for lack of outermost `[...]`, nor will it reject your data for placement
of newlines. The difference is on _output_: using `--ojson`, you get outermost `[...]` and pretty-printed
records; using `--ojsonl`, you get no outermost `[...]`, and one line per record.

## PPRINT: Pretty-printed tabular

Miller's pretty-print format is like CSV, but column-aligned.  For example, compare

<pre class="pre-highlight-in-pair">
<b>mlr --ocsv cat data/small</b>
</pre>
<pre class="pre-non-highlight-in-pair">
a,b,i,x,y
pan,pan,1,0.346791,0.726802
eks,pan,2,0.758679,0.522151
wye,wye,3,0.204603,0.338318
eks,wye,4,0.381399,0.134188
wye,pan,5,0.573288,0.863624
</pre>

<pre class="pre-highlight-in-pair">
<b>mlr --opprint cat data/small</b>
</pre>
<pre class="pre-non-highlight-in-pair">
a   b   i x        y
pan pan 1 0.346791 0.726802
eks pan 2 0.758679 0.522151
wye wye 3 0.204603 0.338318
eks wye 4 0.381399 0.134188
wye pan 5 0.573288 0.863624
</pre>

Note that while Miller is a line-at-a-time processor and retains input lines in memory only where necessary (e.g. for sort), pretty-print output requires it to accumulate all input lines (so that it can compute maximum column widths) before producing any output. This has two consequences: (a) pretty-print output won't work on `tail -f` contexts, where Miller will be waiting for an end-of-file marker which never arrives; (b) pretty-print output for large files is constrained by available machine memory.

See [Record Heterogeneity](record-heterogeneity.md) for how Miller handles changes of field names within a single data stream.

For output only (this isn't supported in the input-scanner as of 5.0.0) you can use `--barred` with pprint output format:

<pre class="pre-highlight-in-pair">
<b>mlr --opprint --barred cat data/small</b>
</pre>
<pre class="pre-non-highlight-in-pair">
+-----+-----+---+----------+----------+
| a   | b   | i | x        | y        |
+-----+-----+---+----------+----------+
| pan | pan | 1 | 0.346791 | 0.726802 |
| eks | pan | 2 | 0.758679 | 0.522151 |
| wye | wye | 3 | 0.204603 | 0.338318 |
| eks | wye | 4 | 0.381399 | 0.134188 |
| wye | pan | 5 | 0.573288 | 0.863624 |
+-----+-----+---+----------+----------+
</pre>

## Markdown tabular

Markdown format looks like this:

<pre class="pre-highlight-in-pair">
<b>mlr --omd cat data/small</b>
</pre>
<pre class="pre-non-highlight-in-pair">
| a | b | i | x | y |
| --- | --- | --- | --- | --- |
| pan | pan | 1 | 0.346791 | 0.726802 |
| eks | pan | 2 | 0.758679 | 0.522151 |
| wye | wye | 3 | 0.204603 | 0.338318 |
| eks | wye | 4 | 0.381399 | 0.134188 |
| wye | pan | 5 | 0.573288 | 0.863624 |
</pre>

which renders like this when dropped into various web tools (e.g. github comments):

![pix/omd.png](pix/omd.png)

As of Miller 4.3.0, markdown format is supported only for output, not input.

## XTAB: Vertical tabular

This is perhaps most useful for looking a very wide and/or multi-column data which causes line-wraps on the screen (but see also
[ngrid](https://github.com/twosigma/ngrid/) for an entirely different, very powerful option). Namely:

<pre class="pre-highlight-in-pair">
<b>$ grep -v '^#' /etc/passwd | head -n 6 | mlr --nidx --fs : --opprint cat</b>
</pre>
<pre class="pre-non-highlight-in-pair">
1          2 3  4  5                          6               7
nobody     * -2 -2 Unprivileged User          /var/empty      /usr/bin/false
root       * 0  0  System Administrator       /var/root       /bin/sh
daemon     * 1  1  System Services            /var/root       /usr/bin/false
_uucp      * 4  4  Unix to Unix Copy Protocol /var/spool/uucp /usr/sbin/uucico
_taskgated * 13 13 Task Gate Daemon           /var/empty      /usr/bin/false
_networkd  * 24 24 Network Services           /var/networkd   /usr/bin/false
</pre>

<pre class="pre-highlight-in-pair">
<b>$ grep -v '^#' /etc/passwd | head -n 2 | mlr --nidx --fs : --oxtab cat</b>
</pre>
<pre class="pre-non-highlight-in-pair">
1 nobody
2 *
3 -2
4 -2
5 Unprivileged User
6 /var/empty
7 /usr/bin/false

1 root
2 *
3 0
4 0
5 System Administrator
6 /var/root
7 /bin/sh
</pre>

<pre class="pre-highlight-in-pair">
<b>$ grep -v '^#' /etc/passwd | head -n 2 | \</b>
<b>  mlr --nidx --fs : --ojson \</b>
<b>    label name,password,uid,gid,gecos,home_dir,shell</b>
</pre>
<pre class="pre-non-highlight-in-pair">
[
{
  "name": "nobody",
  "password": "*",
  "uid": -2,
  "gid": -2,
  "gecos": "Unprivileged User",
  "home_dir": "/var/empty",
  "shell": "/usr/bin/false"
},
{
  "name": "root",
  "password": "*",
  "uid": 0,
  "gid": 0,
  "gecos": "System Administrator",
  "home_dir": "/var/root",
  "shell": "/bin/sh"
}
]
</pre>

## DKVP: Key-value pairs

Miller's default file format is DKVP, for **delimited key-value pairs**. Example:

<pre class="pre-highlight-in-pair">
<b>mlr cat data/small</b>
</pre>
<pre class="pre-non-highlight-in-pair">
a=pan,b=pan,i=1,x=0.346791,y=0.726802
a=eks,b=pan,i=2,x=0.758679,y=0.522151
a=wye,b=wye,i=3,x=0.204603,y=0.338318
a=eks,b=wye,i=4,x=0.381399,y=0.134188
a=wye,b=pan,i=5,x=0.573288,y=0.863624
</pre>

Such data are easy to generate, e.g. in Ruby with

<pre class="pre-non-highlight-non-pair">
puts "host=#{hostname},seconds=#{t2-t1},message=#{msg}"
</pre>

<pre class="pre-non-highlight-non-pair">
puts mymap.collect{|k,v| "#{k}=#{v}"}.join(',')
</pre>

or `print` statements in various languages, e.g.

<pre class="pre-non-highlight-non-pair">
echo "type=3,user=$USER,date=$date\n";
</pre>

<pre class="pre-non-highlight-non-pair">
logger.log("type=3,user=$USER,date=$date\n");
</pre>

Fields lacking an IPS will have positional index (starting at 1) used as the key, as in NIDX format. For example, `dish=7,egg=8,flint` is parsed as `"dish" => "7", "egg" => "8", "3" => "flint"` and `dish,egg,flint` is parsed as `"1" => "dish", "2" => "egg", "3" => "flint"`.

As discussed in [Record Heterogeneity](record-heterogeneity.md), Miller handles changes of field names within the same data stream. But using DKVP format this is particularly natural. One of my favorite use-cases for Miller is in application/server logs, where I log all sorts of lines such as

<pre class="pre-non-highlight-non-pair">
resource=/path/to/file,loadsec=0.45,ok=true
record_count=100, resource=/path/to/file
resource=/some/other/path,loadsec=0.97,ok=false
</pre>

etc. and I just log them as needed. Then later, I can use `grep`, `mlr --opprint group-like`, etc.
to analyze my logs.

See the [separators page](reference-main-separators.md) regarding how to specify separators other than the default equals-sign and comma.

## NIDX: Index-numbered (toolkit style)

With `--inidx --ifs ' ' --repifs`, Miller splits lines on spaces and assigns integer field names starting with 1.

This recapitulates Unix-toolkit behavior.

Example with index-numbered output:

<pre class="pre-highlight-in-pair">
<b>cat data/small</b>
</pre>
<pre class="pre-non-highlight-in-pair">
a=pan,b=pan,i=1,x=0.346791,y=0.726802
a=eks,b=pan,i=2,x=0.758679,y=0.522151
a=wye,b=wye,i=3,x=0.204603,y=0.338318
a=eks,b=wye,i=4,x=0.381399,y=0.134188
a=wye,b=pan,i=5,x=0.573288,y=0.863624
</pre>

<pre class="pre-highlight-in-pair">
<b>mlr --onidx --ofs ' ' cat data/small</b>
</pre>
<pre class="pre-non-highlight-in-pair">
pan pan 1 0.346791 0.726802
eks pan 2 0.758679 0.522151
wye wye 3 0.204603 0.338318
eks wye 4 0.381399 0.134188
wye pan 5 0.573288 0.863624
</pre>

Example with index-numbered input:

<pre class="pre-highlight-in-pair">
<b>cat data/mydata.txt</b>
</pre>
<pre class="pre-non-highlight-in-pair">
oh say can you see
by the dawn's
early light
</pre>

<pre class="pre-highlight-in-pair">
<b>mlr --inidx --ifs ' ' --odkvp cat data/mydata.txt</b>
</pre>
<pre class="pre-non-highlight-in-pair">
1=oh,2=say,3=can,4=you,5=see
1=by,2=the,3=dawn's
1=early,2=light
</pre>

Example with index-numbered input and output:

<pre class="pre-highlight-in-pair">
<b>cat data/mydata.txt</b>
</pre>
<pre class="pre-non-highlight-in-pair">
oh say can you see
by the dawn's
early light
</pre>

<pre class="pre-highlight-in-pair">
<b>mlr --nidx --fs ' ' --repifs cut -f 2,3 data/mydata.txt</b>
</pre>
<pre class="pre-non-highlight-in-pair">
say can
the dawn's
light
</pre>

## Data-conversion keystroke-savers

While you can do format conversion using `mlr --icsv --ojson cat myfile.csv`, there are also keystroke-savers for this purpose, such as `mlr --c2j cat myfile.csv`.  For a complete list:

<pre class="pre-highlight-in-pair">
<b>mlr help format-conversion-keystroke-saver-flags</b>
</pre>
<pre class="pre-non-highlight-in-pair">
FORMAT-CONVERSION KEYSTROKE-SAVER FLAGS
As keystroke-savers for format-conversion you may use the following.
The letters c, t, j, l, d, n, x, p, and m refer to formats CSV, TSV, DKVP, NIDX,
JSON, JSON Lines, XTAB, PPRINT, and markdown, respectively. Note that markdown
format is available for output only.

| In\out | CSV   | TSV   | JSON   | JSONL  | DKVP   | NIDX   | XTAB   | PPRINT | Markdown |
+--------+-------+-------+--------+--------+--------+--------+--------+----------+
| CSV    |       | --c2t | --c2j  | --c2l  | --c2d  | --c2n  | --c2x  | --c2p  | --c2m    |
| TSV    | --t2c |       | --t2j  | --t2l  | --t2d  | --t2n  | --t2x  | --t2p  | --t2m    |
| JSON   | --j2c | --j2t |        | --j2l  | --j2d  | --j2n  | --j2x  | --j2p  | --j2m    |
| JSONL  | --l2c | --l2t |        |        | --l2d  | --l2n  | --l2x  | --l2p  | --l2m    |
| DKVP   | --d2c | --d2t | --d2j  | --d2l  |        | --d2n  | --d2x  | --d2p  | --d2m    |
| NIDX   | --n2c | --n2t | --n2j  | --n2l  | --n2d  |        | --n2x  | --n2p  | --n2m    |
| XTAB   | --x2c | --x2t | --x2j  | --x2l  | --x2d  | --x2n  |        | --x2p  | --x2m    |
| PPRINT | --p2c | --p2t | --p2j  | --p2l  | --p2d  | --p2n  | --p2x  |        | --p2m    |

-p                       Keystroke-saver for `--nidx --fs space --repifs`.
-T                       Keystroke-saver for `--nidx --fs tab`.
</pre>

## Comments in data

You can include comments within your data files, and either have them ignored, or passed directly through to the standard output as soon as they are encountered:

<pre class="pre-highlight-in-pair">
<b>mlr help comments-in-data-flags</b>
</pre>
<pre class="pre-non-highlight-in-pair">
COMMENTS-IN-DATA FLAGS
Miller lets you put comments in your data, such as

    # This is a comment for a CSV file
    a,b,c
    1,2,3
    4,5,6

Notes:

* Comments are only honored at the start of a line.
* In the absence of any of the below four options, comments are data like
  any other text. (The comments-in-data feature is opt-in.)
* When `--pass-comments` is used, comment lines are written to standard output
  immediately upon being read; they are not part of the record stream.  Results
  may be counterintuitive. A suggestion is to place comments at the start of
  data files.

--pass-comments          Immediately print commented lines (prefixed by `#`)
                         within the input.
--pass-comments-with {string}
                         Immediately print commented lines within input, with
                         specified prefix.
--skip-comments          Ignore commented lines (prefixed by `#`) within the
                         input.
--skip-comments-with {string}
                         Ignore commented lines within input, with specified
                         prefix.
</pre>

Examples:

<pre class="pre-highlight-in-pair">
<b>cat data/budget.csv</b>
</pre>
<pre class="pre-non-highlight-in-pair">
# Asana -- here are the budget figures you asked for!
type,quantity
purple,456.78
green,678.12
orange,123.45
</pre>

<pre class="pre-highlight-in-pair">
<b>mlr --skip-comments --icsv --opprint sort -nr quantity data/budget.csv</b>
</pre>
<pre class="pre-non-highlight-in-pair">
type   quantity
green  678.12
purple 456.78
orange 123.45
</pre>

<pre class="pre-highlight-in-pair">
<b>mlr --pass-comments --icsv --opprint sort -nr quantity data/budget.csv</b>
</pre>
<pre class="pre-non-highlight-in-pair">
# Asana -- here are the budget figures you asked for!
type   quantity
green  678.12
purple 456.78
orange 123.45
</pre>
