POKI_PUT_TOC_HERE

<h1>File-format awareness</h1>

Miller respects CSV headers. If you do <tt>mlr --csv cat *.csv</tt> then the header line is written once:

<table><tr>
<td>
POKI_RUN_COMMAND{{cat data/a.csv}}HERE
</td>
<td>
POKI_RUN_COMMAND{{cat data/b.csv}}HERE
</td>
<td>
POKI_RUN_COMMAND{{mlr --csv cat data/a.csv data/b.csv}}HERE
</td>
<td>
POKI_RUN_COMMAND{{mlr --csv sort -nr b data/a.csv data/b.csv}}HERE
</td>
</tr></table>

Likewise with <tt>mlr sort</tt>, <tt>mlr tac</tt>, and so on.

<h1>awk-like features: mlr filter and mlr put</h1>

<ul>

<li/> <tt>mlr filter</tt> includes/excludes records based on a filter
expression, e.g. <tt>mlr filter '$count &gt; 10'</tt>.

<li/> <tt>mlr put</tt> adds a new field as a function of others, e.g. <tt>mlr
put '$xy = $x * $y'</tt> or <tt>mlr put '$counter = NR'</tt>.

<li/> The <tt>$name</tt> syntax is straight from <tt>awk</tt>&rsquo;s <tt>$1 $2
$3</tt> (adapted to name-based indexing), as are the variables <tt>FS</tt>,
<tt>OFS</tt>, <tt>RS</tt>, <tt>ORS</tt>, <tt>NF</tt>, <tt>NR</tt>, and
<tt>FILENAME</tt>. The <tt>ENV[...]</tt> syntax is from Ruby.

<li/> While <tt>awk</tt> functions are record-based, Miller subcommands (or
<i>verbs</i>) are stream-based: each of them maps a stream of records into
another stream of records.

<li/> Like <tt>awk</tt>, Miller (as of v5.0.0) allows you to define new
functions within its <tt>put</tt> and <tt>filter</tt> expression language.
Further programmability comes from chaining with <tt>then</tt>.

<li/> As with <tt>awk</tt>, <tt>$</tt>-variables are stream variables and all
verbs (such as <tt>cut</tt>, <tt>stats1</tt>, <tt>put</tt>, etc.) as well as
<tt>put</tt>/<tt>filter</tt> statements operate on streams.  This means that
you define actions to be done on each record and then stream your data through
those actions.  The built-in variables <tt>NF</tt>, <tt>NR</tt>, etc.  change
from one line to another, <tt>$x</tt> is a label for field <tt>x</tt> in the
current record, and the input to <tt>sqrt($x)</tt> changes from one record to
the next.  The expression language for the <tt>put</tt> and <tt>filter</tt>
verbs additionally allows you to define <tt>begin {...}</tt> and
<tt>end {...}</tt> blocks for actions to be taken before and after records are
processed, respectively.

<li/> As with <tt>awk</tt>, Miller&rsquo;s <tt>put</tt>/<tt>filter</tt>
language lets you set <tt>@sum=0</tt> before records are read, then update that
sum on each record, then print its value at the end.  Unlike <tt>awk</tt>,
Miller makes syntactically explicit the difference between variables with
extent across all records (names starting with <tt>@</tt>, such as
<tt>@sum</tt>) and variables which are local to the current expression (names
starting without <tt>@</tt>, such as <tt>sum</tt>).

<li/> Miller can be faster than <tt>awk</tt>, <tt>cut</tt>, and so on,
depending on platform; see also POKI_PUT_LINK_FOR_PAGE(performance.html)HERE).
In particular, Miller&rsquo;s DSL syntax is parsed into C control structures at
startup time, with the bulk data-stream processing all done in C.

</ul>

<h1>See also</h1>

<p/>See POKI_PUT_LINK_FOR_PAGE(reference.html)HERE for more on Miller&rsquo;s
subcommands <tt>cat</tt>, <tt>cut</tt>, <tt>head</tt>, <tt>sort</tt>,
<tt>tac</tt>, <tt>tail</tt>, <tt>top</tt>, and <tt>uniq</tt>, as well as awk-like
<tt>mlr filter</tt> and <tt>mlr put</tt>.
