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57 lines
1.9 KiB
HTML
57 lines
1.9 KiB
HTML
POKI_PUT_TOC_HERE
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<h1>File-format awareness</h1>
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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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POKI_RUN_COMMAND{{cat a.csv}}HERE
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</td>
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<td>
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POKI_RUN_COMMAND{{cat b.csv}}HERE
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</td>
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<td>
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POKI_RUN_COMMAND{{mlr --csv cat a.csv b.csv}}HERE
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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>
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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 POKI_PUT_LINK_FOR_PAGE(performance.html)HERE). 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>
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<p/>See POKI_PUT_LINK_FOR_PAGE(reference.html)HERE 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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