Re: Document [Austin-117:XCU:m4 maketemp, mkstemp Proposed] created

[Eric Blake]

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According to Eric Blake on 10/7/2006 4:33 PM:
> In line with the two aardvarks I just filed against mkstemp(3), I propose
> this wording for the mkstemp paragraph in interpretation 117 (the rest of
> the proposed solution is fine as is):
> 
> Insert new macro immediately after maketemp
> 
>  mkstemp   The first argument shall be taken as a template for creating an
> empty file, with trailing 'X' characters replaced with characters from the
> portable file name set.  The behavior is unspecified if the first argument
> does not end in at least six 'X' characters.  If a temporary file is
> successfully created, then the defining text of the macro is the name of
> the new file; the file is owned by the effective user and group of the
> process, and the file access permission bits are set such that only the
> owner can both read and write the file, regardless of the current umask of
> the process.  If a file could not be created, the defining text of the
> macro shall be the empty string.
> 

Reviving an old thread, but in implementing mkstemp in GNU m4, I realized
that there is a very slight chance that the file name generated by mkstemp
can happen to match a defined macro name.  As written, the interp makes it
sound like mkstemp should produce an unquoted file name, but in the event
of the random overlap, that means that the rescan of the filename will
expand the macro, and the user is left with a different string than the
name of the file that was just created, but only on rare occasions, which
makes for a very difficult situation to debug.

I'm thinking that it would be much nicer to require the mkstemp macro to
result in quoted output, so that the rescan of the output strips the quote
and leaves the name of the file just created, regardless of any potential
macro names already defined.  This would mean changing:

If a temporary file is successfully created, then the defining text of the
macro is the name of the new file;

to

If a temporary file is successfully created, then the defining text of the
macro is the quoted name of the new file;

My inspection of several existing m4 implementations shows that maketemp
has always produced unquoted output, but since no file was created and
this macro has been obsoleted, this is less likely to cause actual
problems in user scripts.  Therefore, I see no reason to change maketemp.

- --
Don't work too hard, make some time for fun as well!

Eric Blake             address@hidden
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