my $match1 = "^$datestring\s+\d{2}:\d{2}:\d{2},\d{3}\s+-\s+\d{2}:\d{2}:\d{2},\d{3}\s+$SLEVEL1";
use Data::Dumper;
$Data::Dumper::Useqq=1;
print Dumper($match1);

__END__

$VAR1 = "^2017-01-04s+d{2}:d{2}:d{2},d{3}s+-s+d{2}:d{2}:d{2},d{3}s+ERROR";