GNU Parallel

		https://www.gnu.org/software/parallel/


= Presentation of GNU Parallel =

GNU Parallel is a shell tool for executing jobs in parallel using one
or more computers. A job can be a single command or a small script
that has to be run for each of the lines in the input. The typical
input is a list of files, a list of hosts, a list of users, a list of
URLs, or a list of tables. A job can also be a command that reads from
a pipe. GNU Parallel can then split the input and pipe it into
commands in parallel.

If you use xargs and tee today you will find GNU Parallel very easy to
use as GNU Parallel is written to have the same options as xargs. If
you write loops in shell, you will find GNU Parallel may be able to
replace most of the loops and make them run faster by running several
jobs in parallel.

GNU Parallel makes sure output from the commands is the same output as
you would get had you run the commands sequentially. This makes it
possible to use output from GNU Parallel as input for other programs.

See the cheat sheet for examples that cover most of the daily usage:
www.gnu.org/s/parallel/parallel_cheat.pdf


= 10 seconds installation =

For security reasons it is recommended you use your package manager to
install. But if you cannot do that then you can use this 10 seconds
installation.

The 10 seconds installation will try to do a full installation; if
that fails, a personal installation; if that fails, a minimal
installation.

    $ (wget -O - pi.dk/3 || lynx -source pi.dk/3 || curl pi.dk/3/ || \
       fetch -o - http://pi.dk/3 ) > install.sh
    $ sha1sum install.sh | grep 3374ec53bacb199b245af2dda86df6c9
    12345678 3374ec53 bacb199b 245af2dd a86df6c9
    $ md5sum install.sh | grep 029a9ac06e8b5bc6052eac57b2c3c9ca
    029a9ac0 6e8b5bc6 052eac57 b2c3c9ca
    $ sha512sum install.sh | grep f517006d9897747bed8a4694b1acba1b
    40f53af6 9e20dae5 713ba06c f517006d 9897747b ed8a4694 b1acba1b 1464beb4
    60055629 3f2356f3 3e9c4e3c 76e3f3af a9db4b32 bd33322b 975696fc e6b23cfb
    $ bash install.sh

This will literally install faster than reading the rest of this
document.


= Full installation =

Full installation of GNU Parallel is as simple as:

    wget https://ftpmirror.gnu.org/parallel/parallel-20200622.tar.bz2
    wget https://ftpmirror.gnu.org/parallel/parallel-20200622.tar.bz2.sig
    gpg parallel-20200622.tar.bz2.sig
    bzip2 -dc parallel-20200622.tar.bz2 | tar xvf -
    cd parallel-20200622
    ./configure && make && sudo make install


= Personal installation =

If you are not root you can add ~/bin to your path and install in
~/bin and ~/share:

    wget https://ftpmirror.gnu.org/parallel/parallel-20200622.tar.bz2
    wget https://ftpmirror.gnu.org/parallel/parallel-20200622.tar.bz2.sig
    gpg parallel-20200622.tar.bz2.sig
    bzip2 -dc parallel-20200622.tar.bz2 | tar xvf -
    cd parallel-20200622
    ./configure --prefix=$HOME && make && make install

Or if your system lacks 'make' you can simply copy src/parallel
src/sem src/niceload src/sql to a dir in your path.


= Minimal installation =

If you just need parallel and do not have 'make' installed (maybe the
system is old or Microsoft Windows):

    wget https://git.savannah.gnu.org/cgit/parallel.git/plain/src/parallel
    chmod 755 parallel
    cp parallel sem
    mv parallel sem dir-in-your-$PATH/bin/


= Installation on compute servers =

If you are developing your script to run on a remote server, that does
not have GNU Parallel installed, but you have it installed on you
development machine, the use can use `parallel --embed`.

    parallel --embed > newscript.sh

Just edit the last lines of newscript.sh and copy it to the compute
server.


= Test the installation =

After this you should be able to do:

    parallel -j0 ping -nc 3 ::: qubes-os.org gnu.org freenetproject.org

This will send 3 ping packets to 3 different hosts in parallel and print
the output when they complete.

Watch the intro video for a quick introduction:
https://www.youtube.com/playlist?list=PL284C9FF2488BC6D1

Walk through the tutorial (man parallel_tutorial). You command line
will love you for it.

When using programs that use GNU Parallel to process data for
publication please cite:

    Tange, O. (2020, June 22). GNU Parallel 20200622 ('Floyd').
    Zenodo. https://doi.org/10.5281/zenodo.3903853


= New versions =

New versions will be released at: https://ftp.gnu.org/gnu/parallel/


= Dependencies =

GNU Parallel should work with a normal full Perl installation. However,
if you system has split up Perl into multiple packages then these are
the important ones:

    opkg install perlbase-getopt perlbase-ipc procps-ng-ps perlbase-mime