Re: [bug] globify dospath reacts poorly with escaped double quotes

[Brian Inglis <Brian.Inglis@SystematicSw.ab.ca>]

On 2019-10-08 03:05, Mingye Wang wrote:
> This bug is inherited from early versions of Cygwin. It's so old that
> MSYS2 has this problem too.

Probably not a bug then but a feature for Cygwin.
Msys2 is another system with different goals, using GNU toolchains to build
native Windows programs, not a platform for running POSIX applications like
Cygwin, and OT for this list.

> There is no way of conveying a double quote in an argument once
> globify() decides it has seen a dospath. Neither the `\"` nor `""`
> work, because they are both unified to `\"` in quoted() and turned
> into a `\\` pattern in globify().

Msys2 tools have to make their own arrangements if they support native Windows
paths.
Personally I found when I used to use DOS and Windows tools, it was easier using
slashes instead of backslashes as directory separators, as most interfaces did
not care, including most DOS & Windows APIs.

> This is problematic for programmers trying to write a routine to
> reliably escape an argument for the Cygwin command-line.

Backslash escaping and switching enclosing quotes on shell command lines works
reliably to pass any arguments into Cygwin programs, as do the various shell
command line parameter and wildcard expansions.
Passing special characters into arguments interpreted by other programs requires
additional care.

> A way to patch the problem is with a lookahead in globify():
> 
> if (dos_spec && *s == '\\') {
> /**/p++ = '\\';
> /**/if (s[1] == '"' && s[2]) {
> /****/*p = *++s;
> /****/continue;
> /**/}
> }
> *p = *s;
> 
> [Apologies for the formatting; the gmail web editor hates leading spaces.]
> 
> (Note: The backslash thing has always been different from the MSCRT
> handling, which only transforms backslashes followed by a double
> quote. But this is fine as long as we are internally consistent.
> Well... is it documented anywhere?)

Support of DOS paths is inconsistent in Cygwin utilities and may not work: use
cygpath, or the low level API, to convert DOS to POSIX paths before passing to
Cygwin programs, or functions.

Backslash should only be used to escape command line characters with special
meaning to the shell, or escapes in strings in other languages.

Any other use should specify what kinds or arguments ypu are trying to handle,
how you are getting your arguments in, and passing them to globify.

Invoking Cygwin programs from other Cygwin programs is best done using the exec
or spawn functions with (unescaped, unquoted) arguments in varargs arg lists or
arrays.

Invoking Windows programs works best when done from a cmd wrapper, but anything
involving any Windows command line requires work to generalize.
See previous recent posts for what is required.

Avoid system() and similar calls if possible, as they will then go thru an
additional shell layer.

-- 
Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada

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