PowerShell's call operator (&) syntax and double-quotes

Question

Can someone explain this result to me? I've wasted a lot of time over the years trying to master PowerShell's syntax for calling commands, but this...I can't even make a guess how to get this result from the input.

PS C:\Users\P> & echoargs "   ""1"" 2 3 ""4 5 6""   7 8 9"
Arg 0 is <   1 2 3 4>
Arg 1 is <5>
Arg 2 is <6   7 8 9>

Bueller?

Answer 1

The doubled-up doubles quotes inside a double-quoted string is a way to insert a double quote. The updated version of echoargs.exe shows this a bit more clearly as it shows you the command line used to invoke the exe:

PS>  echoargs "   ""1"" 2 3 ""4 5 6""   7 8 9"
Arg 0 is <   1 2 3 4>
Arg 1 is <5>
Arg 2 is <6   7 8 9>

Command line:
"C:\...\Modules\Pscx\Apps\EchoArgs.exe"  "   "1" 2 3 "4 5 6"   7 8 9"

If you take that command line (after it has been parsed by PowerShell) you get the same result in CMD.exe:

CMD> EchoArgs.exe "   "1" 2 3 "4 5 6"   7 8 9"
Arg 0 is <   1 2 3 4>
Arg 1 is <5>
Arg 2 is <6   7 8 9>

Command line:
C:\...\Modules\Pscx\Apps\EchoArgs.exe  "   "1" 2 3 "4 5 6"   7 8 9"

As to why .NET or the C++ startup code parses the command line that way, I'm not entirely sure. This MSDN topic covers it a bit and if you look at the examples at the bottom of the topic, you will see some equally weird parsing behavior e.g. a\\\b d"e f"g h gives a\\\b, de fg and h.

Answer 2

Note that Powershell is known for some heavy bugs when it comes to passing arguments to applications and quoting the said arguments - http://connect.microsoft.com/PowerShell/feedback/details/376207/executing-commands-which-require-quotes-and-variables-is-practically-impossible

This is how I understand how it is being (mis)parsed:

The string is " ""1"" 2 3 ""4 5 6"" 7 8 9"

Because of the bug the double double quotes, which become literal double quote, never make it.

The string would be like " "1" 2 3 "4 5 6" 7 8 9"

So <space>1 2 3 4 becomes an argument because it the first section with matching quotes and 4 occurs before the next space. Then space, and hence 5 becomes second argument. Then space, so the next part will be a separate argument. Here again, the same rule as the first argument, except that 6 occurs before quote and without a space and hence 6 7 8 9 becomes the next argument.

Bottomline - Powershell argument passing to external applications is pretty messed up.