Table of Contents

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Basicly it calls ‘cat <f_in> | <command> > <f_out>’. When <f_in> is empty, then it runs <command> > <f_out> and when <f_out> is empty, then it ‘cat <f_in> | <command>’.

<command> can be also a pipeline. If <f_in> is partitioned, then <command> is applied on all partitions and keep the output <f_out> also partitioned.


  <f_in> <f_out> <command>

evl cmd
  ( --help | --usage | --version )


Standard options:


print this help and exit


print short usage information and exit

-v, --verbose

print to stderr info/debug messages of the component


print version and exit


  1. Write 10 times ’repeat some error message’ to the STDERR and into EVL job log:
    Cmd "" /dev/stderr "yes repeat some error message | head"

2. Suppose from ‘SOME_FLOW’ we obtain integers, one by line, then median can be obtained from R and be written into ‘/some/file’:

Cmd SOME_FLOW /some/file "Rscript median.R"

The file median.R might look like this:

f <- file('stdin'); open(f); x <- c(); 
while ( length( line <- readLines(f) ) > 0 ) x <- c(x,as.integer(line));
write(median(x), stdout());