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Re: m4 macro expansion problem
From: |
Zack Weinberg |
Subject: |
Re: m4 macro expansion problem |
Date: |
Wed, 25 Aug 2021 14:41:19 -0400 |
User-agent: |
Cyrus-JMAP/3.5.0-alpha0-1125-g685cec594c-fm-20210825.001-g685cec59 |
On Wed, Aug 25, 2021, at 12:06 PM, Sébastien Hinderer wrote:
> Zack Weinberg (2021/08/25 11:39 -0400):
> > m4_syscmd is a primitive, and it doesn't expand its argument, so you need
> > to expand PKG_VERSION first:
> >
> > m4_syscmd([cat > VERSION << \END_OF_VERSION_FILE
> > ]PKG_VERSION[
> >
> > # Some comments about the format of version numbers
> > END_OF_VERSION_FILE
> > ])
> I double-checked my code and there was no \ before END_OF_VERSION_FILE
> and the code was working so may I ask why you added one in your code?
That's an extra defensive measure. It makes the *shell* treat the here
document as quoted, so that if your PKG_VERSION or your commentary ever happens
to contain shell metacharacters they won't do anything surprising. I
habitually add this to here documents unless there's a reason to *want* shell
variable expansion (for instance) in some particular here document.
zw
Re: m4 macro expansion problem, Peter Johansson, 2021/08/23