use 'P' parameter expansion flag with array?

use 'P' parameter expansion flag with array?

[Greg Klanderman]

If the 'P' parameter expansion flag is applied to an array parameter,
should it be applied to each of the elements?  Seems like it should,
but it doesn't seem to be:


[~] greg@lwm| zsh -f
lwm% 
lwm% echo $ZSH_VERSION
4.3.10-dev-1
lwm% foo=(bar baz)
lwm% bar=10
lwm% baz=35
lwm% echo ${(P)foo}
10
lwm% echo ${(P@)foo}
10
lwm% echo ${(P)foo[@]}
10
lwm% 


thanks,
Greg

Re: use 'P' parameter expansion flag with array?

[Peter Stephenson]

Greg Klanderman wrote:
> If the 'P' parameter expansion flag is applied to an array parameter,
> should it be applied to each of the elements?

It does seem logical, but the code is obscure and it's not clear whether
this was intended or not---it probably fell through the cracks.  I don't
think the flag was completely thought through in other ways I've noticed
in the past, though I've forgotten what they are for the time being.
paramsubst() is full of my "one day someone should spend a year tidying
this up" comments.

-- 
Peter Stephenson <pws@csr.com>                  Software Engineer
CSR PLC, Churchill House, Cambridge Business Park, Cowley Road
Cambridge, CB4 0WZ, UK                          Tel: +44 (0)1223 692070

Re: use 'P' parameter expansion flag with array?

[Greg Klanderman]

> It does seem logical, but the code is obscure and it's not clear whether
> this was intended or not---it probably fell through the cracks.

Thank you Peter, I'll just use a loop then..

> paramsubst() is full of my "one day someone should spend a year tidying
> this up" comments.

Yeah I enjoyed reading a number of those last night after sending
that question  :-)

So if I have an array and want to append a string to each of the
elements, then join with colon, is there a better way than this:

lwm% a=(x y z)
lwm% echo ${(j.:.)${(@)a/%/foo}}
xfoo:yfoo:zfoo

I was trying to do something using '^' but it doesn't seem to work;

lwm% echo ${(@)^a}foo
xfoo yfoo zfoo

does what I expect, but:

lwm% echo ${(j.:.)${(@)^a}foo}
zsh: bad substitution

does not.

thanks,
Greg

Re: use 'P' parameter expansion flag with array?

[Mikael Magnusson]

2009/6/30 Greg Klanderman <gak@klanderman.net>:
>
>> It does seem logical, but the code is obscure and it's not clear whether
>> this was intended or not---it probably fell through the cracks.
>
> Thank you Peter, I'll just use a loop then..
>
>> paramsubst() is full of my "one day someone should spend a year tidying
>> this up" comments.
>
> Yeah I enjoyed reading a number of those last night after sending
> that question  :-)
>
> So if I have an array and want to append a string to each of the
> elements, then join with colon, is there a better way than this:
>
> lwm% a=(x y z)
> lwm% echo ${(j.:.)${(@)a/%/foo}}
> xfoo:yfoo:zfoo
>
> I was trying to do something using '^' but it doesn't seem to work;
>
> lwm% echo ${(@)^a}foo
> xfoo yfoo zfoo
>
> does what I expect, but:
>
> lwm% echo ${(j.:.)${(@)^a}foo}
> zsh: bad substitution
>
> does not.

echo ${(j.:.):-${(@)^a}foo}
will work fine, the simplest case of the error is this, i think:
% echo ${${}foo}
zsh: bad substitution
% echo ${:-${}foo}
foo

-- 
Mikael Magnusson

Re: use 'P' parameter expansion flag with array?

[Greg Klanderman]

>>>>> Mikael Magnusson <mikachu@gmail.com> writes:

> echo ${(j.:.):-${(@)^a}foo}

Thank you Mikael!  I really need a zsh cheat-sheet..

greg

Re: use 'P' parameter expansion flag with array?

[Bart Schaefer]

On Jun 30,  9:43am, Peter Stephenson wrote:
}
} Greg Klanderman wrote:
} > If the 'P' parameter expansion flag is applied to an array parameter,
} > should it be applied to each of the elements?
} 
} It does seem logical, but the code is obscure and it's not clear whether
} this was intended or not---it probably fell through the cracks.

The (P) flag was supposed to create an approximate equivalent of ksh
"nameref" parameters.  Because of the way array expansion operates in
ksh and similar shells, extending (P) to an automatic "map" over an
array wasn't considered.