Re: Quoting special characters (was: Re: Possible solution for special characters in makefile paths)

[Tim Murphy]

Just to throw something into the mix.  I would quite like this:

$(file fred/alice/bob one.txt)

...which would always expand to $(file fred/alice/bob one.txt) other
than in a recipe or in any place which implements file-related
functions such as checking timestamps etc.

I think it would be nice to know which targets are real files and
which aren't anyhow.

Regards,

Tim

On 23 February 2014 23:11, Frank Heckenbach <address@hidden> wrote:
> Paul Smith wrote:
>
>> On Sat, 2014-02-22 at 22:18 +0100, Frank Heckenbach wrote:
>> > The problem is how to quote them for a command line. In bash (and I
>> > think any POSIX shell, but I'm not even sure of that), you can quote
>> > an arbitrary string, but not in a uniform way. There are several
>> > ways to do that, the simplest one (AFAIK) is to put '' around the
>> > string and handle ' within the string specially (close the ', quote
>> > the actual ' with a \, start a new ' quote for the rest of the
>> > string, because \ does not escape within ''; therefore the
>> > Q='$(subst ','\'',$(1))' in my previous mail).
>>
>> Actually, for POSIX sh the simplest thing to do in general is just add a
>> backslash before any special character.  In fact in shell if you don't
>> mind doubling the size of your string you can just backslash-escape
>> EVERY character and be sure you're getting exactly the right thing.
>
> And if you don't mind making your command-lines absolutely
> unreadable. It might be a minor concern, but if we do something like
> this by default, and make runs (and echoes) a simple compile command
> like this, though technically correct, people might think we're
> crazy. ;)
>
> \c\c \-\W\a\l\l -o \f\o\o.o \f\o\o.c
>
>> But usually we just escape the ones that are special :-).
>
> Which adds more dependency on the type of shell (which characters
> are special).
>
>> However for writing a make function, using backslashes is a more complex
>> solution (requires multiple nested subst functions, one for each special
>> character) and single-quotes is easier.
>
> Indeed, without regex (or some other form of character-set)
> replacements, this gets heavy.
>
> But these are all details. In any case, it is possible to escape any
> given string to POSIX sh.
>
>> > Yet, as I said, I'd like to see a solution to this problem. So even
>> > if it's not possible in a fully automatic way, the next best thing
>> > is to require as little user intervention as possible. This might be
>> > achieved with a special variable, let's call it SHELL_QUOTE, which
>> > has a similar status as SHELL and is applied when expanding a
>> > variable into a command line -- separately for each word of it(!),
>> > and of course also for automatic variables such as $@, $< or $^.
>> >
>> > Unfortunately, SHELL_QUOTE couldn't be set by default because it
>> > would break commands with manual quoting
>>
>> I was thinking about this, but I was just thinking of having a hardcoded
>> behavior that would be applied whenever you were using a POSIX-y shell
>> but could be enabled or disabled or something.
>>
>> At first glance I was not sure about your suggestion, but on further
>> thought it does have a lot to like about it: for example by using a
>> variable it can have the same scope as SHELL and be set in a
>> target-specific variable for a given rule, etc.  It's certainly more
>> flexible.
>
> That's the idea. (I hadn't thought about target-specific variables,
> but it's another pro.)
>
>> I do wonder about performance but I guess construction of a
>> command line to run a recipe is not a performance-critical part of the
>> code.
>
> Probably not, but it's actually somewhat more efficient than having
> the user do all the quoting manually (cf. my other mail).
>
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