Re: escaped newline in macro expansion in command line

[Humm]

(woops, sorry for replying off-list first; mutt doesn’t like me)

Quoth Paul Smith:
> In your example the backslash is part of a variable expansion: it's
> INSIDE the variable expansion so it will be handled by make as part of
> expanding the variable and won't ever be passed to the shell.

POSIX.1-2017 says about this (98624-98631):

> When an escaped <newline> (one preceded by a <backslash>) is found 
> anywhere in the makefile except in a command line, an include line, 
> or a line immediately preceding an include line, it shall be 
> replaced, along with any leading white space on the following line, 
> with a single <space>. When an escaped <newline> is found in 
> a command line in a makefile, the command line shall contain the 
> <backslash>, the <newline>, and the next line, except that the first
> character of the next line shall not be included if it is a <tab>.  
> When an escaped <newline> is found in an include line or in a line 
> immediately preceding an include line, the behavior is unspecified.

So per POSIX, it doesn’t matter in what specific context an escaped 
newline is, it only matters in what sort of line it is, even if it is 
in a macro expansion.

> It's handled as if you wrote:
>
>  M = word
>  _X = ${M:word=a\
>  b
>
>  all: ; echo ${_X}
>
> Where you would expect to see "a b".

Here, the escaped newline is in a macro definition line, and thus 
replaced by a blank before defining _X as “${M:word=a b”.

> There is an argument to be made that the backslash should be managed as
> if it were part of a command line and not part of a variable assignment
> because it appears in a recipe, even though it's part of a make
> variable expansion.

That’s the argument I’m making.

> If the backslash were handled that way then make
> would see this:
>
>  echo ${M:word=ab}
>
> after the backslash/newline was removed and it would run the command:
>
>  echo ab
>
> which is still not
>
>  echo a\
>  b
>
> but would give equivalent output in this case.

Nope, it wouldn’t remove the escaped newline, it would pass it to the 
shell, which would then elide it.

        all:
                echo 'a\
                b'

passes to the shell

        echo 'a\
        b'

which outputs

        a\
        b

This, gmake handles right (and bmake—the other make I have right here 
to test—does not).

--
Humm