Then-chaining

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In accord with the Unix philosophy, you can pipe data into or out of Miller. For example:

<pre class="pre-highlight-non-pair"> <b>mlr cut --complement -f os_version *.dat | mlr sort -f hostname,uptime</b> </pre>

You can, if you like, instead simply chain commands together using the then keyword:

<pre class="pre-highlight-non-pair"> <b>mlr cut --complement -f os_version then sort -f hostname,uptime *.dat</b> </pre>

(You can precede the very first verb with then, if you like, for symmetry.)

Here's a performance comparison:

<pre class="pre-non-highlight-non-pair"> % cat piped.sh mlr cut -x -f i,y data/big | mlr sort -n y &gt; /dev/null % time sh piped.sh real 0m2.321s user 0m4.878s sys 0m1.564s % cat chained.sh mlr cut -x -f i,y then sort -n y data/big &gt; /dev/null % time sh chained.sh real 0m2.070s user 0m2.738s sys 0m1.259s </pre>

There are two reasons to use then-chaining: one is for performance, although I don't expect this to be a win in all cases. Using then-chaining avoids redundant string-parsing and string-formatting at each pipeline step: instead input records are parsed once, they are fed through each pipeline stage in memory, and then output records are formatted once.

The other reason to use then-chaining is for simplicity: you don't have re-type formatting flags (e.g. --csv --fs tab) at every pipeline stage.

As of Miller 6.3.0, + is an alias for then.