Re: singleton for script with shebang

[Ole Tange]

On Fri, Jan 2, 2015 at 8:14 AM, Shlomi Fish <shlomif@shlomifish.org> wrote:
> On Thu, 1 Jan 2015 13:54:57 -0800
> Bradley Asztalos <brad@customweather.com> wrote:
:
>> [... shebang ...]
>
> parallel is written in Perl 5 and uses «#!/usr/bin/perl» or whatever as a
> shebang. As a result it cannot be itself used as a she-bang processor.

So why is Shlomi right, when it is clearly possible to use GNU
Parallel as shebang program?

It is because on some UNIX systems this is actually true. On FreeBSD
you need to do:

  #!/usr/bin/env -S parallel --shebang-wrap ...

On other UNIXes there is no work around.

> Furthermore, I should note that in programming, it is a good idea to stick to
> the https://en.wikipedia.org/wiki/KISS_principle and not try to be as clever 
> as
> possible.

Sometimes the code is simpler if GNU Parallel is put in the shebang
line. But it does carry some limitations. The length of the shebang
line is quite limited on many systems, and often the systems will
simply chop it off without any warning.

See http://www.in-ulm.de/~mascheck/various/shebang/#length


/Ole