Preferences, how to specify

[Pierre Dupond <76nemo76%gmx.ch@localhost>]

Hi All,
     At many place I see mentions of specifying preferences
for some part of PKGSRC.

Unfortunately, even if I have looked at many places (Web, pkgsrc site, man page), I have
not found documentation about the specifying of the preferences or examples of their usage.

If I pass the command "bootstrap --help" I get the following output
and one can notice that it seems possible to specify preferences.

Usage: ./bootstrap
    [ --abi [32|64] ]
    [ --binary-kit <tarball> ]
    [ --binary-macpkg <pkg> ]
    [ --compiler <compiler> ]
    [ --cwrappers <auto|yes|no> ]
    [ --full ]
    [ --gzip-binary-kit <tarball> ]
    [ --help ]
    [ --make-jobs <num> ]
    [ --mk-fragment <mk.conf> ]
    [ --pkgdbdir <pkgdbdir> ]
    [ --pkginfodir <pkginfodir> ]
    [ --pkgmandir <pkgmandir> ]
    [ --prefer-pkgsrc <list|yes|no> ]
    [ --prefix <prefix> ]
    [ --preserve-path ]
    [ --quiet ]
    [ --sysconfdir <sysconfdir> ]
    [ --unprivileged | --ignore-user-check ]
    [ --varbase <varbase> ]
    [ --workdir <workdir> ]

I have not succeeded however to specify some preferences nor to list
what preferences can be specified. By the way, I have not found
documentation about some of the parameters of the "bootstrap"
command (for instance --cwrappers, --compiler <compiler>, --full).

It will be probably useful to prefer some tools (like "libtools") of the underlying distribution
since using (and doing the recompilation which is sometime quite complicated) the similar/same tools
of PKGSRC is sometime very difficult and ever time consuming.

I hope I have not missed some obvious documentation and I would appreciate if
somebody could give me some pointers on how to use the preferences system.

Thanks,
--
Gmail <76nemo76%gmx.ch@localhost>