Code:
$text = "This is not good,\n you know what I mean?\n\nThis should be on a separate line.";
$text =~ s/[^\n]\n[^\n]//g;
print $text;

Run:
C:\Perl>perl test.pl
This is not goodyou know what I mean?

This should be on a separate line.

Should Print:
This is not good, you know what I mean?

This should be on a separate line.