@a=(11,22,33,44,55);
@b=(22,44,66,17);
foreach (@a) # $_ gets one value from @a
{
  @tested=grep {$_ == $::_} @b; # Had $_ been lexical for grep, $::_ would've been a global
}
print "\n@tested"; #Doesn't work as expected...$_ and $::_ both are same and get each value from @b