Re: Forcing expansion without explicit eval nor a subshell?

[Lloyd Zusman <ljz@xxxxxxxxxx>]

Bart Schaefer <schaefer@xxxxxxxxxxxxxxxx> writes:

> On Nov 4, 11:01pm, Lloyd Zusman wrote:
> } Subject: Forcing expansion without explicit eval nor a subshell?
> }
> } Suppose I have the following variable defined:
> } 
> }   yumargs='--disablerepo=livna{,-updates,-testing,-extras}'
> } 
> } I want to assign to "yumargs" exactly as I did above, if possible, and
> } I'm looking for some combination of modifiers within the ${} construct
> } which would give me the expansion of "yumargs" that I desire, and
> } without the need for a subshell.  And I'd like the expansion of
> } "yumargs" to take place at the time it is used in the "yum" command, not
> } at the time that I define it.
> } 
> } Is all this possible?  If so, could someone give me a hint or pointer?
>
> Given all the restrictions you've placed, no, it's not possible.  There
> is no parameter-expansion modifier to force brace expansion.
>
> If you relax the "exactly as above" restriction, you could do this:
>
> yumargs=( --disablerepo=livna{,-updates,-testing,-extras} )
>
> That is, make yumargs be an array of four strings rather than a single
> string that contains a brace expression.  I'm unable to see a reason why
> it would matter when the brace expansion is performed; but if you think
> it's important to defer it, you're going to be stuck with eval.

I want to defer it in case I do this:

  yumargs='--disablerepo={dag,$livnastuff}'

... where $livnastuff can change, and where it might or might not
involve more brace expansions.  But that's really idiosyncratic, and I
guess I'll just live with having to use "eval".

Thanks a lot for your help.


-- 
 Lloyd Zusman
 ljz@xxxxxxxxxx
 God bless you.