processing data from stdin

[Mike Miller]

Just thought I'd share something.  I was going to submit a question, but 
then I figured out the answer on my own, so I'll just submit an answer. 
;-)

I have a process that sends a space-delimited matrix to stdout.  I want 
octave to grab that matrix, do some operations on it, and send output to 
stdout.  Here is an example process that produces an N-by-3 matrix.

egrep -h '^[0-9]' file*.txt | gawk '{print $1" "$2" "$3}'

I want to perform an operation such as "mean" on that matrix.  I'm using 
tcsh shell and I came up with this solution:

( echo 'X= [' ; \
egrep -h '^[0-9]' file*.txt | gawk '{print $1" "$2" "$3}' ; \
echo '];' ; echo 'disp(mean(X))' ) | octave -q

It works from the command line, or in a script.  The initial and final 
parentheses hold stdout in a subshell so that commands separated by 
semi-colons produce only a single stdout.  Without the "octave -q" on the 
end, you would see something like this:

X= [
1 1 1
1 0 1
];
disp(mean(X))

That is piped to Octave and a single row vector is sent by Octave to 
stdout.  It's pretty neat, thanks to Octave!

Mike

--
Michael B. Miller, Ph.D.
Assistant Professor
Division of Epidemiology
and Institute of Human Genetics
University of Minnesota
http://taxa.epi.umn.edu/~mbmiller/



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