Actually, in this case the space is being added, not by the output field separator ($,), but by the list separator ($"), because the array slice is stringified. To get what you want, you can either (1) set $" to the empty string (not undef, that gives a warning), or (2) not stringify the array slice in the print statement:

16:14 >perl -wE "my @array = qw(abc def ghi jkl mno); print @array[2,4
+], qq{\n};"
ghimno

16:14 >
[download]

See the entries for $" and $, in perlvar.

Hope that helps,