Re: config files substitution with awk

[Paolo Bonzini]

> Note that it must be done carefully, since we could have:
>
> s/@var1@/@var2@/g
> s/@var2@/text2/g
>
> and @var1@ in the input would sustitute to text2.

Right.  sed, however, does not collapse the DFAs in such a way and 
there's no intention of the maintainer (me :-) to add this optimization.

> So we must still have as many DFAs as s commands, but with some luck,
> we can skip directly to the right action. (For this reason, I'd
> suggest to use a more specific tool rather than sed which is too
> general for this job).

In fact, awk can be the appropriate tool.

> Given the regexps r1, r2, ... rn in the n 's' commands, we can build
> the first DFA as:
>
>   r1|r2|r3|....|rn

This can be implemented using a single regular expression /@address@hidden@/ plus 
an associative array lookup.

> The second DFA would be:  r2|r3|...|rn

I think you would have to loop the full r1|r2|r3|....|rn DFA in order to 
mimic the previous behavior of autoconf (though I don't have the source 
code handy).

Paolo