Extra assignment

[n9]

@mgkuhn

julia/base/strings/io.jl

Line 622 in cc345f6

escapes = 0

Is this assignment needed?

Update: I have just found a closed PR for this: #38499
I can't see the build details to see why it failed. (It shows empty screen.)

[mgkuhn]

No, that line can be deleted from escape_raw_string.

It probably was a leftover from a previous draft of the algorithm, e.g. one that may have used write(io, '\\' ^ escapes) instead of while escapes > 0; write(io, '\\'); escapes -= 1; end. Given Julia's use of unbuffered standard output #43176, I'm still not sure in such situations whether I should minimize the number of allocations or the number of write calls and methods used.

[n9]

Thank you for your answer. This will also answer my second question, whether this algorithm is currently equivalent to:

function escape_raw_string(io, str::AbstractString)
    for c in str
        if c in ('\\', '"')
            write(io, '\\')
        end
        write(io, c)
    end
end

If yes, I was wondering, why the code is currently complicated.

[mgkuhn]

That's a different algorithm that is incompatible with how Julia raw string escaping works.

[mgkuhn]

It's more like how POSIX shell escaping works rather than how Microsoft C escaping command-line parameter escaping works. (In other words, it is more sane. Julia raw strings went with the less sane Microsoft C approach, which is not a homomorphism under string concatenation.)

[n9]

Ok. I have to download Julia and try them both:) My in-brain running skill seems to fail.

[n9]

Could you please provide me a case where both algorithms return different results? (I am unable to find one.)

[n9]

... Nevermind, I have found one: "c:\\Program Files\\".

[mgkuhn]

Since we are looking at escape_raw_string again: one thing I had on my todo list was to extend this function (e.g., with two optional arguments escapes = Ref{Int}(0), last = true) such that it can be used in streaming mode. If you have a multi-gigabyte string that you want to escape into a raw string, you may want to do this without holding the entire string in memory, processing just chunks at a time. To enable this, we'd need:

• a way to preserve the escapes value across invocations (perhaps by making it a reference argument?)
• a way to tell the function if it is processing the last chunk in a sequence of string chunks (because after the last chunk, it must reduce escapes to zero)

So when I make a PR for that, I'll also delete that line.

[n9]

I have one more question regarding this function. Why this function is not used around dir in pushd?

julia/stdlib/Distributed/src/managers.jl

Line 312 in cc345f6

remotecmd = "pushd \"$(dir)\" && $remotecmd"

[n9]

Make sense, thank you! (Maybe the surrounding quotes are also not needed there.)

[mgkuhn]

These quotes are needed by cmd.exe to disable other meta characters that might occur in the filename (such as the && that follows). I've tested this routine quite carefully to correctly treat all allowed characters in Windows filenames.

[mgkuhn]

If you think I got something wrong, please provide an example.

[mgkuhn]

In case you are trying to understand this code to port it elsewhere: my advice is to keep in mind that Windows command-line syntax is wild and crazy, and that nothing you might expect from being familiar with POSIX shells will apply. After a lot of time, reading and experimentation, I think I have mastered most of cmd.exe syntax, but I am still really struggling to e.g. make sense of PowerShell syntax, which seems even worse ...

The main reason why I still haven't finished the PowerShell option of the launch_on_machine function is that the safest option I found so far is to invoke cmd.exe from PowerShell. (Widely used PowerShell versions have no equivalent of &&.)

[n9]

In case you are trying to understand this code to port it elsewhere ...

I am just trying to invoke Windows executable via SSH command (noninteractively).

... keep in mind that Windows command-line syntax is wild and crazy ...

Yes, currently, the only documentation I have found is this: https://docs.microsoft.com/en-us/archive/blogs/twistylittlepassagesallalike/everyone-quotes-command-line-arguments-the-wrong-way

... but I am still really struggling to e.g. make sense of PowerShell syntax, which seems even worse ...

I came here from PowerShell/Win32-OpenSSH#1082.