Re: confused by m4 esyscmd expansion ... how to 'escape' nested quotes?

[OpenMacNews]

hi stepan,

i think i'm getting the hang of m4 -- very cool! (in case you haven't guessed, 
i'm new to it ...)

so, one more step ...

first,

(1) prior advice works great!

> since you already use awk, it's probably best to use printf instead of print.
>
> And awk can also search for the right line.  If I understand the
> format of the output of DiG correctly, it would be
>
>     changequote([,])
>     define([MY_IP_ADDR],
>           esyscmd([dig @my.ns.domain.com machine.domain.com |
>                 awk 'index($ 0, "machine.domain.com") == 1 {
>                         printf("%s", $ 5) }']))

> This will work with any reasonable awk.

works perfectly!

fwiw (& hth others ...):

% which awk
   /usr/local/bin/awk
% awk --version
   GNU Awk 3.1.4
% uname -a
   Darwin devbox 8.2.0 Darwin Kernel Version 8.2.0: Fri Jun 24 17:46:54 PDT 
2005; root:xnu-792.2.4.obj~3/RELEASE_PPC Power Macintosh powerpc



(2) now, one FURTHER iteration -- confusion again:

in my next steps of building my httpd.conf.m4 template, i'm facing an issue w/ 
nesting of VARIABLES ...


now, i'd like to reference an earlier-defined variable INTERNAL to m4.  in 
principle:

        changequote([,])
        define([MY_NS_NAME],         [ns.domain.com])
        define([MY_HOST_NAME],       [machine.domain.com])

        define([MY_IP_ADDR],
       esyscmd([dig @MY_NS_NAME MY_HOST_NAME |
       awk 'index($ 0, "MY_HOST_NAME") == 1 {
       printf("%s", $ 5) }']))

but, with this, on processing, i get an error:

        dig: couldn't get address for 'MY_NS_NAME': not found

clearly, the var 'MY_NS_NAME' is not being passed ...


reading further @:

        http://www.gnu.org/software/m4/manual/m4.html#Indir

       which results in a call to the macro name, which is passed the rest of
       the arguments. This can be used to call macros with “illegal” names
       (define allows such names to be defined):
           define(`$$internal$macro', `Internal macro (name `$0')')
           =>
           $$internal$macro
           =>$$internal$macro
           indir(`$$internal$macro')
           =>Internal macro (name $$internal$macro)

, i guessed that 'indir' might be my solution with:

        changequote([,])
        define([$$MY_NS_NAME],         [ns.domain.com])
        define([$$MY_HOST_NAME],       [machine.domain.com])
        define([MY_IP_ADDR],
       esyscmd([dig @indir[$$MY_NS_NAME] indir[$$MY_HOST_NAME] |
       awk 'index($ 0, "indir[$$MY_HOST_NAME]") == 1 {
       printf("%s", $ 5) }']))

but this results in:

        dig: couldn't get address for 'indir[1914MY_NS_NAME]': not found

if indir IS my solution (is it?), then, again, i'm fairly sure i've got the "$" 
syntax screwed-up ...


cheers,

richard