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

From: OpenMacNews
Subject: Re: confused by m4 esyscmd expansion ... how to 'escape' nested quotes?
Date: Sat, 06 Aug 2005 09:55:30 -0700

hi stepan,

A few examples:


the step-through + examples are *very* helpful, thx!

Does it make sense now?

i thought it did; but, here's the current status/result --

starting with:

        define([MY_DNS_NAME],         [ns.mydomain.com])
        define([MY_HOST_NAME],        [machine.mydomain.com])

(a) this WORKS as expected

[esyscmd(dig @indir([MY_DNS_NAME]) indir([MY_HOST_NAME]) | grep indir([MY_HOST_NAME]) | grep -v DiG | grep -v ";"indir([MY_HOST_NAME]) | awk '{printf("%s", $ 5) }')])

expanding "", without a CR, into all instances of MY_IP_ADDR in my template (e.g., "httpd.conf.m4")

(b) this, does NOT work:

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

resulting in:

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

(c) this, does NOT work:

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

resulting in:

        -->  sh: -c: line 1: syntax error near unexpected token `('
sh: -c: line 1: `dig @indir([MY_DNS_NAME]) indir([MY_HOST_NAME]) | awk 'index($ 0, "indir([MY_HOST_NAME])") == 1 {printf("%s", $ 5) }''

(d) this, does NOT work:

(NOTE my 'quoting' here is similar to case(a), which does work ...)

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

resulting in:

        -->  Usage: awk [POSIX or GNU style options] -f progfile [--] file ...
             Usage: awk [POSIX or GNU style options] [--] 'program' file ...
             POSIX options:          GNU long options:
             -f progfile             --file=progfile
             -F fs                   --field-separator=fs


(a) works.  which is good!
(b) & (c) *may* be instances of awk not 'liking' the DNS "dig" output, rather than an m4 issue -- tho i'm not immediately certain of that ...
(d) raises the question of the DIFFERENCE in quoting between:

        define([...],esyscmd([dig ...           (which you'd recommmended ...)


        define([...],[esyscmd(dig ...           (which seems to work 4 me ...)

so i need to read further & play with some local trial-n-error.


It's difficult for the authors of the documentation to
understand how the text will be seen by newcomers' eyes...)

i admit being that 'newcomer', and _very much_ appreciate the recognition that --even WITH googling and RTFM'ing -- that sometimes it's a bit confusing to get started.

far too often, imho, folks on lists simply get 'nasty' if you ask a question that THEY know the answer to and feel you should too ... which i find so incredibly ironic.

If yes, perhaps you could contribute to the
GNU m4 documentation, so that future readers don't go through the same

that said, i'd be happy to contribute what i can -- when *I* figure it out myself! :-), and expand my macro to supporting multiple domain/IP discovery -- with a commented, practical example.

personally, i think using/mod'ing apache's conf is a commonplace enuf tast that folks might follow the example much more readily/capably than the somewhat simplistic/obscure (too me, that is) "examples" in the man page.

the general issue with such examples is that they too often limit their scope to simply the package at hand ... e.g., "only" within "m4" scope.

but, practical application -- as in my case -- typically includes the integration of, say, m4+awk+apache.

if find that your kind help is atypical (<-- good thing!) in that you're willing to both (a) work with a newcomer and (b) work 'outside' of 'your app'.

this, also, is a general challenge in integration across ANY two open-source apps -- lots of finger pointing, and associated "try another list" comments.

i will be the first to agree that RTFM'ing is absolutely the right appraoch to any one package ... but, honestly, when you're trying to make 10, 20 or more 'things' work together, it seldom readily solves the problem.

rather, help from patient, more experienced folks, does.  =)




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