With POSIX support I meant the libc and lower portions of POSIX and I was under the impression that e.g POSIX exec() was part of whatever was once enough to give Microsoft some claim of POSIX compatibility certifications for NT and later. Looks like I badly misremembered things.

My original question is the reverse of your example:

Can I e.g. set $ENV{VARIABLE} in a non-CYGWIN-port of Perl, and then use system q{dir "%VARIABLE%"} to have cmd.exe expand the variable? More specifically, what happens if the variable contains [\n \\;"']?

A new question/request:

What I'd love to do is appending a link to a node giving the comparable portable (or windows) version of $ENV{f}="a b; 'c'"; system q{dir "\$f"}.

Alternately at most a single concise paragraph as a footnote on the windows side of things to Re: *SAFE* use of string in system command.
Otherwise its a bit unfair if the Unix view hogs all the good keywords and doesn't help a windows SoPW :)

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What I currently have - after some searching on PerlMonks - is a mess and a headache (and a bit of glee in lacking the windows environment to test this mess).

It reads like system/exec/(pipe-)open should be avoided on Windows for non-trivial commands, preferring IPC::System::Simple or Win32::Process::Create instead.

• asychronnous system(1,...) magic to replace start (windows) or a final '&' (unix).
• lack of fork(): What is the difference between Windows fork an Unix fork ?, with a mismatched substitute in Win32::Process
  (archived copy of Mr. Peabody Explains fork())
• Construct command portable way
• Perl Background processes in Windows
• How to Start a Process in a Remote Win32 Machine using Perl and WMI
• help needede in backticks(``) and system function
• Non-shell-invoking system/exec and qx//
• Windows command line; incl. cmd.exe quoting surprises

Do we have a better explanation or tutorial already on PerlMonks or do you know of a suitable resource outside?
Merci!