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List:       exim-users
Subject:    Re: [exim] Single quotes and transport_filter
From:       Jeremy Harris via Exim-users <exim-users () exim ! org>
Date:       2023-03-19 18:23:14
Message-ID: 6855c921-0f32-4a3e-e4aa-f226645b1271 () wizmail ! org
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On 19/03/2023 17:22, Ian Z via Exim-users wrote:
> Chapter 24 documents the transport_filter option. An example is given
> where the argv vector for the command comes from an expansion:
> 
>    transport_filter = '/bin/cmd${if eq{$host}{a.b.c}{1}{2}}'
> 
>    This runs the command /bin/cmd1 if the host name is a.b.c, and
>    /bin/cmd2 otherwise. If double quotes had been used, they would have
>    been stripped by Exim when it read the option's value.  When the
>    value is used, if the single quotes were missing, the line would be
>    split into two items, /bin/cmd${if and eq{$host}{a.b.c}{1}{2}, and
>    an error would occur when Exim tried to expand the first one.
> 
> I have two problems grokking this:
> 
> - I can  find no other place in the spec where it is specifically
>    explained what single quotes do, as opposed to double quotes.

Yup; this could be better.

In the coding I find an explanatory comment:

/* Split the command up into arguments terminated by white space. Lose
trailing space at the start and end. Double-quoted arguments can contain \\ and
\" escapes and so can be handled by the standard function; single-quoted
arguments are verbatim. Copy each argument into a new string. */

> 
> - In Section 29.3 on pipe commands (which are supposedly expanded the
>    same way), there is this example:
> 
>      command = /some/path ${if eq{$local_part}{postmaster}{xx}{yy}}
> 
>      will not work, because the expansion item gets split between
>      several arguments.  You have to write
> 
>      command = /some/path "${if eq{$local_part}{postmaster}{xx}{yy}}"
> 
>    So why are double quotes OK here?

The difference is an artefact of the option-handling described in
Ch.6 Sec.17 :-  if an option value *starts* with a doublequote
then it must end with one (and, implicitly, they get stripped
at that processing phase.  The pipe example does not.

-- 
Cheers,
   Jeremy


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