BSS <blah blah>
   SSID: <ssid>
   <blah blah>
BSS <and so on>

##</code><code>##

my $out = qx| sudo iw dev wlan0 scan |;
$out .= "\nBSS";

my @chunks = $out =~ /^(BSS.*?)(?=^BSS)/smg;

my @essids = map { /SSID: (.*?)$/ms; $1 } @chunks;