Re: Random string generation during *-install

[Jean-Yves Migeon <jeanyves.migeon%free.fr@localhost>]

Le 25/05/2015 13:15, Taylor R Campbell a écrit :
>     Date: Mon, 25 May 2015 01:31:01 +0200
>     From: Jean-Yves Migeon <jeanyves.migeon%free.fr@localhost>
>
>     Le 24/05/2015 20:47, Kamil Rytarowski a écrit :
>     > Once I had to do something similar in a shell script and replace bash(1)
>     > $RANDOM with a portable alternative.
>     >
>     > I went for awk(1), initial ideas are at http://awk.info/?tip/random
>
> Beware that most programming languages' built-in random number
> generators are lousy, and totally unfit for applications requiring
> unpredictability.  E.g., if your application is a network daemon
> requiring an unpredictable secret random seed, you cannot use awk's
> rand safely to generate it.

Yep, those examples are downright dangerous if you need crypto quality 
randomness. However I do think they are ok to generate distinct 
identifiers upon building of my ill-conceived app.

>     Thanks. I ended up using urandom and tr(1) and delete any non printable
>     char, not quite perfect but does an ok job.
>
> That's what I would recommend.
>
> (tr -cd '[:graph:]' | head -c 20) < /dev/urandom
>
> There's a slim chance that on some exotic Unixoid platform pkgsrc
> supports, you can't assume there will be a /dev/urandom.  But I
> wouldn't worry about it until someone actually trips over it.

That's almost what I did, the only difference being that I "LC_ALL=C" 
right before calling tr. On some platform it tries to parse /dev/urandom 
bytes as UTF-8 encoded strings (as per locale) and tr(1) chokes when 
encoding is invalid.

>     >> What is the correct way of generating a fixed random string on
>     >> pre-install or do-install stage?
>     [...]
>     BTW is there a way to add arbitrary commands to a pkginstall's INSTALL
>     script? Just wondering whether binary packages would add even more
>     restrictions to the environment (not needed in my present scenario, but
>     alas, sooner or later...)
>
> Don't use pre-install and do-install for this -- use the INSTALL
> script alongside the Makefile.  The pre-install and do-install make
> targets are always (unless you explicitly set USE_DESTDIR=no, which is
> ill-advised) run at build-time when installing into a destdir before
> creating a package, not at install-time when you actually install the
> package.

This is what the pkgsrc's guide says, but alas it does not say what I am 
supposed to do to patch in some code in INSTALL. So what would be the 
recommended way to alter a pkginstall INSTALL script when generated by 
the templates? Does that mean someone(tm) has to "manually" patch 
WRKSRC/.pkginstall/INSTALL?

Cheers,

--
Jean-Yves Migeon