my $test_str = 'C:\VENDOR\MICROSOFT\PLATFORMSDK\INCLUDE' ;
my ( $first, $second ) = $test_str =~ m/^([^\\]+\\[^\\]+)(\\.*)$/ ;
print "first: $first\nsecond: $second\n" ;

# first: C:\VENDOR
# second: \MICROSOFT\PLATFORMSDK\INCLUDE