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Re: patsubst: multiline text

From: Eric Blake
Subject: Re: patsubst: multiline text
Date: Mon, 06 Sep 2010 15:34:13 -0600
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On 09/06/2010 09:57 AM, clemens fischer wrote:
My problem is with the newlines in the text, I'm unable to match the
portions before and after them.  I already tried a number of
combinations, with and without literal newlines in {regex}, using eg.
{^\(.+?\)\n} or {^\(.+?\)\\n} or {^\([^\\n]\)+} for {regex}, but the
statements in m4.info referring to the emacs regex syntax seem to need
qualification, so to speak.  I've also tried to "define({_nl_},<literal
newline here>)" or using that literal directly, nothing helps.

Thanks for the question.

Unfortunately, there is admittedly a problem with the current regex implementation - it is line based, rather than argument based, so you can't really get at newlines directly. Ultimately, the right fix is to add another argument to the various regex macros that lets you set flags (line vs. argument, case insensitive, maybe others?) for how a given regex will behave.

On the other hand, since it is all line based, it may be easier than you think. First, note that this inserts spaces on every line:

patsubst({ml_text}, {^}, {  })

Then, if you concatenate text before the first line, then a second pass can clean up the first line:

patsubst({-}patsubst({{ml_text}}, {^}, {  }), {^-  }, {- })

(Untested, but hopefully gives you enough ideas).

Eric Blake   address@hidden    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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