|From:||M Douglas McIlroy|
|Subject:||Re: Is it possible to expand macro just once?|
|Date:||Mon, 12 Oct 2020 21:28:10 -0400|
On 10/12/20 5:27 AM, Wolf wrote:
> Not subscribed to the list, so please CC.
That's standard practice anyway ;)
> I have m4 template that contains macro, that I do not know the value of
> (provided by user). That can lead to user setting the macro to name of
> another macro, like:
> $ echo foo | m4 -Dfoo=bar -Dbar=baz
> Now, I understand why it happens and that it is expected. However, due
> to reason stated above, I need the macro to expand just once, so that
> the snippet above would produce `bar`. Is there a way to do so?
In general, if the user is providing you text rather than something that
should expand as a macro that needs further recursive interpretation,
you should use defn() to get at that text:
$ echo 'changequote([,])defn([foo])' | m4 -Dfoo=bar -Dbar=baz
But keep in mind that defn does NOT perform any interpolation of $,
which may introduce its own oddities if the user supplied a macro
definition containing $ that you aren't expanding as a macro.
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
Virtualization: qemu.org | libvirt.org
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