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May 19, 2015 - A Look At The New Commandlinefu
I've put together a short writeup on what kind of newness you can expect from the next iteration of clfu. Check it out here.
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grep (or anything else) many files with multiprocessor power

Terminal - grep (or anything else) many files with multiprocessor power
find . -type f -print0 | xargs -0 -P 4 -n 40 grep -i foobar
2009-08-05 23:18:44
User: ketil
Functions: find grep xargs
grep (or anything else) many files with multiprocessor power

xargs -P N spawns up to N worker processes. -n 40 means each grep command gets up to 40 file names each on the command line.


There are 9 alternatives - vote for the best!

Terminal - Alternatives
find . -type f | parallel -j+0 grep -i foobar
2010-01-30 02:08:46
Functions: find grep

Parallel does not suffer from the risk of mixing of output that xargs suffers from. -j+0 will run as many jobs in parallel as you have cores.

With parallel you only need -0 (and -print0) if your filenames contain a '\n'.

Parallel is from https://savannah.nongnu.org/projects/parallel/

Know a better way?

If you can do better, submit your command here.

What others think

Since grep is mostly IO-bound, I doubt it will benefit much from running in parallel.

Comment by spatz 377 weeks ago

I don't see how the "-n 40" is needed nor relevant. Any clarification on why you use that?

Comment by linuxrawkstar 376 weeks and 6 days ago

the xargs man page *specifically* recommends using the -n with -P, and explains why...

Comment by eichin 376 weeks ago

The xargs version risks lines being mixed:

Assume you have two files with matching lines that are grepped by each their process and that these lines are long. You then have a race condition with a risk of getting a mixed output like this:

start_of_line_from_file1 line_from_file2

end_of_line_from file1

The Parallel version does not suffer from this.

Comment by unixmonkey8046 351 weeks and 5 days ago

Yes, I guess the output could be interleaved in some cases (perhaps lines longer than BUFSIZ). It seems parallel does some input/output trickery to avoid this. It can also force output order to be the same as the input order, despite tasks finishing out of order.

But this is only an issue if the result of the executed program is output to stdout. If your program writes somewhere else, or does something else entirely, xargs (which is probably more common) does the trick.

Comment by ketil 351 weeks ago

Your point of view

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