Re: GNU Parallel

[Ole Tange]

On Fri, Sep 5, 2014 at 8:36 PM, Stephan Kuschel
<stephan.kuschel@uni-jena.de> wrote:

> Dear Mr. Tange,

Please use parallel@gnu.org for support. This way you can get input
from other users and do not depend on me answering your questions.

> i am using gnu parallel (thanks for the great tool!)

If you like GNU Parallel:

* Give a demo at your local user group/team/colleagues

* Post the intro videos and the tutorial on Reddit, Diaspora*, forums,
blogs, Identi.ca, Google+, Twitter, Facebook, Linkedin, mailing lists

* Request or write a review for your favourite blog or magazine

* Invite me for your next conference

If you use GNU Parallel for research:

* Please cite GNU Parallel in you publications (use --bibtex)

If GNU Parallel saves you money:

* (Have your company) donate to FSF https://my.fsf.org/donate/

> and I was wondering
> why its not possible to use -u and --tag at the same time (-u will make
> the tag disappear, although it would be particularly useful in this
> case, i think.).

As mentioned in the man page:

    --tag is ignored when using -u.
[...]
    It also disables --tag.

> Compare:
> parallel --tag echo ::: 1 2 3
> parallel -u --tag echo ::: 1 2 3
>
> Is there a specific reason for that?

The technical reason is that normally output is processed by GNU
Parallel by sending it to temporary files and reading these back when
data is output, but using -u this processing is disabled. So GNU
Parallel does not "see" the output at all and thus cannot change it.

You have not specified why you need -u, but most people using -u
really mean --line-buffer. And --line-buffer can be run with --tag.

There is a speed penalty to have GNU Parallel look at the output.
Compare the speed of these:

  parallel seq ::: 300000000 >/dev/null
  parallel -u seq ::: 300000000 >/dev/null
  parallel --line-buffer seq ::: 300000000 >/dev/null

> I am using parallel Version 20140822 running at arch linux.
>
> Sorry to bother you with this, google didnt yield any results on this
> question.

I encourage you to use parallel@gnu.org in the future.

> Thanks in advance
> Stephan

/Ole