my $starter = qr{    s    }xsm;  # starts with this string
my $never   = qr{    s    }xsm;  # never starts with this string
my $ender   = qr{ e [ ] p }xsm;  # ends with this string

my $start_line       = qr{ ^     $starter  [^\n]* \n }xsm;
my $intervening_line = qr{ ^ (?! $never )  [^\n]* \n }xsm;
my $end_line         = qr{                 $ender \n }xsm;

my $line = do { local $/;  <DATA> };  # slurp all the data

$line =~ s{ $start_line $intervening_line* $end_line }
          {}gxsm;

print $line;

__DATA__
Random String
s
erartt
e p
s
foo
e f
blah blah
s
adflkja
wibble wobble
e p
End of file

##</code><code>##

Random String
s
foo
e f
blah blah
End of file