7 00:00:30,008 --> 00:00:30,066 by line 8 00:00:31,038 --> 00:00:34,050 or later in the nineteen seventies it was usually a 9 00:00:34,005 --> 00:00:38,634^M video consul but the council was not capable of displaying arbitrate graphics 10 The above lines is in a file named 2.txt. I wanna the lines which doesn't start with number. In practice, sed -i '/^[0-9]+/d' 2.txt works good. However, sed -i '/^\d+/d' 2.txt doesnot. The \d shouldn't be equal to [0-9] in regex?