The updates don't help any. The question I asked in my original post remains. How can you tell where a file name ends? What you ask is not possible, unless you impose extra restrictions. Let's say the file contains the line:

C:\Program Files\Application Name\bin\app.exe > C:\Program Files\Appli
+cation Name\log\app.log do_it 2> C:\Program Files\Foo Bar\log\app.log
[download]

Should the above return:

C:\Progra~1\Applic~1\bin\app.exe > C:\Progra~1\Applic~1\log\applog~1 2
+> C:\Progra~1\FooBar~1\log\app.log
[download]

Probably not. You probably wanted:

C:\Progra~1\Applic~1\bin\app.exe > C:\Progra~1\Applic~1\log\app.log do
+_it 2> C:\Progra~1\FooBar~1\log\app.log
[download]

ok, so you might say you'll never place arguments between redirects (although it would be a exception to what you said you allow). What if the file contained the line:

C:\Program Files\Application Name\bin\app.exe ola c:\file1 ole c:\file
+2
[download]

Should the above return:
C:\Progra~1\Applic~1\bin\appexe~1 c:\file1o~1 c:\file2
or
C:\Progra~1\Applic~1\bin\app.exe ola c:\file1o~1 c:\file2
or
C:\Progra~1\Applic~1\bin\app.exe ola c:\file1 ole c:\file2
Probably not the first, but there's no way to know between the bottom two. It depends on what app.exe expects.

That's why I recommended you quote your paths:

sub quote   { local $_=$_[0]; s/(["\\])/\\$1/g; qq{"$_"} }
sub unquote { local $_=$_[0]; s/^"(.*)"$/$1/ or return $_; s/\\(.)/$1/
+g; $_ }

while (<IN>)
{
   @items = /("(?:[^"\\]|\\.)+"|[^"\s]+)/g;
   foreach (@items) {
      $_ = unquote($_);
      print(Win32::GetShortPathName($_) || quote($_), ' ');
   }

   print("\n");
}
[download]

But that's not all! What the file doesn't exist? It's impossible to get the short file name of a file that doesn't yet exist!