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163 lines
5.7 KiB
HTML
163 lines
5.7 KiB
HTML
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<title> Miller features in the context of the Unix toolkit </title>
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The background image is from a screenshot of a Google search for "data analysis
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tools", lightened and sepia-toned. Over this was placed a Mac Terminal app with
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very light-grey font and translucent background, in which a few statistical
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Miller commands were run with pretty-print-tabular output format.
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<center><titleinbody>Miller</titleinbody></center>
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<br/>User info:
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<br/>• <a href="index.html">About</a>
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<br/>• <a href="file-formats.html">File formats</a>
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<br/>• <a href="feature-comparison.html">Miller features in the context of the Unix toolkit</a>
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<br/>• <a href="record-heterogeneity.html">Record-heterogeneity</a>
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<br/>• <a href="performance.html">Performance</a>
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<br/>• <a href="etymology.html">Why call it Miller?</a>
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<br/>• <a href="originality.html">How original is Miller?</a>
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<br/>• <a href="reference.html">Reference</a>
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<br/>• <a href="data-examples.html">Data examples</a>
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<br/>• <a href="to-do.html">Things to do</a>
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<br/>Developer info:
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<br/>• <a href="build.html">Compiling, portability, dependencies, and testing</a>
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<br/>• <a href="whyc.html">Why C?</a>
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<br/>• <a href="contact.html">Contact information</a>
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<br/>• <a href="https://github.com/johnkerl/miller">GitHub repo</a>
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<br/> <br/> <br/> <br/> <br/> <br/> <br/> <br/> <br/> <br/> <br/> <br/>
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<br/> <br/> <br/> <br/> <br/> <br/> <br/> <br/> <br/> <br/> <br/> <br/>
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<br/> <br/> <br/> <br/> <br/> <br/>
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</div>
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</td>
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<td>
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<center> <titleinbody> Miller features in the context of the Unix toolkit </titleinbody> </center>
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<p>
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<div class="pokitoc">
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<center><b>Contents:</b></center>
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• <a href="#File-format_awareness">File-format awareness</a><br/>
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• <a href="#awk-like_features:_mlr_filter_and_mlr_put">awk-like features: mlr filter and mlr put</a><br/>
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• <a href="#See_also">See also</a><br/>
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</div>
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<p/>
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<h1>File-format awareness</h1> <a id="File-format_awareness"/>
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Miller respects CSV headers. If you do <tt>mlr --csv-input cat *.csv</tt> then the header line is written once:
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<table><tr>
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<td>
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<p/>
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<div class="pokipanel">
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<pre>
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$ cat a.csv
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a,b,c
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1,2,3
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4,5,6
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</pre>
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</div>
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<p/>
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</td>
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<td>
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<p/>
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<div class="pokipanel">
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<pre>
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$ cat b.csv
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a,b,c
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7,8,9
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</pre>
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</div>
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<p/>
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</td>
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<td>
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<p/>
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<div class="pokipanel">
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<pre>
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$ mlr --csv cat a.csv b.csv
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a,b,c
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1,2,3
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4,5,6
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7,8,9
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</pre>
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</div>
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<p/>
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</td>
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</tr></table>
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Likewise with <tt>mlr sort</tt>, <tt>mlr tac</tt>, and so on.
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<h1>awk-like features: mlr filter and mlr put</h1> <a id="awk-like_features:_mlr_filter_and_mlr_put"/>
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<ul>
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<li/> <tt>mlr filter</tt> includes/excludes records based on a filter
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expression, e.g. <tt>mlr filter '$count > 10'</tt>.
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<li/> <tt>mlr put</tt> adds a new field as a function of others, e.g. <tt>mlr
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put '$xy = $x * $y'</tt> or <tt>mlr put '$counter = NR'</tt>.
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<li/> The <tt>$name</tt> syntax is straight from <tt>awk</tt>’s <tt>$1 $2
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$3</tt> (adapted to name-based indexing), as are the variables <tt>FS</tt>,
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<tt>OFS</tt>, <tt>RS</tt>, <tt>ORS</tt>, <tt>NF</tt>, <tt>NR</tt>, and
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<tt>FILENAME</tt>.
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<li/> While <tt>awk</tt> functions are record-based, Miller subcommands (or
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functions, if you like) are stream-based: each of them maps a stream of records
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into another stream of records.
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<li/> Unlike <tt>awk</tt>, Miller doesn’t allow you to define new functions.
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Its domain-specific languages are limited to the <tt>filter</tt> and
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<tt>put</tt> syntax. Futher programmability comes from chaining with
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<tt>then</tt>.
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<li/> Miller is faster than <tt>awk</tt>, <tt>cut</tt>, and so on (depending on
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platform; see also <a href="performance.html">Performance</a>). In
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particular, Miller’s DSL syntax is parsed into C control structures at
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startup time, with the bulk data-stream processing all done in C.
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</ul>
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<h1>See also</h1> <a id="See_also"/>
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<p/>See <a href="reference.html">Reference</a> for more on Miller’s
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subcommands <tt>cat</tt>, <tt>cut</tt>, <tt>head</tt>, <tt>sort</tt>,
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<tt>tac</tt>, <tt>tail</tt>, <tt>top</tt>, and <tt>uniq</tt>, as well as awk-like
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<tt>mlr filter</tt> and <tt>mlr put</tt>.
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</td>
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</table>
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</body>
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</html>
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