Your start version seems to work for me?

[0] Perl> system q[cmd /c del errors output];;
[0] Perl> system q[start /b perl -le"print for 1..10; die 'An error';"
+ 2>errors 1>output];;
[0] Perl> system q[cmd /c type errors output];;

errors


An error at -e line 1.

output


1
2
3
4
5
6
7
8
9
10
[download]