$ perl -Mstrict -Mwarnings -e ' my ($STX, $ETX) = (chr(2), chr(3)); my $re = qr{ [$STX] ( [^$ETX]{0,80} ) [^$ETX]* [$ETX] }x; my $empty = $STX . $ETX; my $short = $STX . "a" x 79 . $ETX; my $exact = $STX . "a" x 80 . $ETX; my $long = $STX . "a" x 81 . $ETX; my $buf = $empty . $short . $exact . $long; print "1234567890" x 8, "\n"; print "$_\n" for $buf =~ /$re/g; print "1234567890" x 8, "\n"; ' 12345678901234567890123456789012345678901234567890123456789012345678901234567890 aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa 12345678901234567890123456789012345678901234567890123456789012345678901234567890