$var =~ /n\\(.?)\\/ <BR>
[download]

matches for "n\" optionally followed by any character followed by a backslash

$var =~ /n\\([^\\])/ <BR>
[download]

matches for n\ not followed by backslash (only one character)
but does also not work for : "/n\123\uu

IMHO following should work better:

$var =~ /n\\([^\\]+)\\/
[download]

MP