use Data::Dumper;
$string = "sp Hello there sp \n Hey hey sp How are you? sp I need a dsp chip and have a spelling test.";
@results = $string =~ m/\bsp\s+(.*?)\s+sp\b/g;
print Data::Dumper->Dump([\@results]);

__OUTPUT__

$VAR1 = [
          'Hello there',
          'How are you?'
        ];