[Development] [Interest] Executing PowerShell command with quotes using QProcess

[Sze Howe Koh]

On 3 April 2014 06:23, Thiago Macieira <thiago.macieira at intel.com> wrote:
> Em qua 02 abr 2014, às 12:18:59, Jason Kretzer escreveu:
>>     powershellHDD.start("PowerShell -Command \"&{(Get-WmiObject
>> Win32_LogicalDisk -Filter \\\"DeviceID='C:'\\\").Size}\"");
>
>> This does not work as I expect it to.  The dataHDDsize is an empty string
>> "".  If I pull the command out and run it directly from a command prompt
>> (removing the escaping backslashes) it runs exactly as I expect it to
>> returning a number.   I thought maybe the number is the problem and I have
>> similar commands that return proper letters and the same thing occurs.
>>
>> Style and suggestions for third party libs aside, does any one have any
>> pointers?
>
> There's a comment in qprocess.cpp that reads:
>
>     // handle quoting. tokens can be surrounded by double quotes
>     // "hello world". three consecutive double quotes represent
>     // the quote character itself.
>
> I don't know whose idea it was to use three quotes successively to indicate a
> quote character. It doesn't work on a regular Unix shell:
>
> $ echo """hello"""
> hello
>
> Nor on Windows's prompt:
> C:\>echo """hello"""
> """hello"""
>
> That commit has been there since the Qt public history started. It's even
> documented as such (I had to look it up, I didn't know):
>         http://qt-project.org/doc/qt-5/qprocess.html#start-3
>
> But I don't know why it was done like that. It's highly surprising. If it
> weren't documented, I'd be tempted to just change behaviour and go for
> standard backslashing.

That's highly unintuitive. The fact that it's Windows-only suggests
that it was put in to work around some issue (which may not be present
in modern versions of Windows). Candidate for change in Qt 6?


Regards,
Sze-Howe