On Saturday 01 August 2009 11:22:41 Steven J Long wrote:
> Mike Frysinger wrote:
> > On Tuesday 21 July 2009 06:13:25 Steven J Long wrote:
> >> Nikos Chantziaras wrote:
> >> > Thanks.  I ended up doing it this way, though with only one loop in
> >> > src_install(), which seems to be a bit more efficient and shorter:
> >> >
> >> >
> >> > LANGUAGES="de"
> >> > for i in ${LANGUAGES}; do
> >> > IUSE="${IUSE} linguas_${i}"
> >> > done
> >>
> >> Just on a side-note (not saying it's how you want to do this one), this
> >> is something that BASH arrays are nice for (saving another loop):
> >> $ foo=(bar baz quux)
> >> $ echo "prefixed: '${foo[*]/#/pfx_}'"
> >> prefixed: 'pfx_bar pfx_baz pfx_quux'
> >
> > printf would probably be better as it is typically a shell builtin and it
> > doesnt require use of arrays/uncommon syntax.
> > media-gfx/exiv2/exiv2-0.18.ebuild:
> > IUSE_LINGUAS="de es fi fr pl ru sk"
> > IUSE="${IUSE} $(printf 'linguas_%s ' ${IUSE_LINGUAS})"
>
> Doh, forgot about printf. (We have alias print="printf '%s\n'" in our lib
> code which comes in handy too.) Nice one.
>
> The only issue with the above is that it requires a subshell; forking isn't
> cheap (especially on Interix/cygwin/doze) and in general it's considered a
> bit lame (at least amongst the ##bash old-timers that I bump heads with) to
> need forking in BASH, though ofc not in SH, which is why it might not be
> the best here, since the metadata generation phase is a restricted subset
> of SH, leave alone BASH, at least aiui.

forks are cheap on any sane *nix box, and subshells/builtins are better than 
external programs.  i'm pretty sure the overhead here tends to be less than 
the overhead of running for loops, especially as the LINGUAS gets bigger.
-mike