flex : regular expression for accepting only numbers, letters , white spaces

Question

I want to write a regular expression to check string that contains only letters,digits,spaces,# and the string length should be minimum 10 and maximum 29 and string should not begin with blank.

please help me

Answer 1

This is one possible regular expression, but I don't know flex:

/^[a-zA-Z0-9#][a-zA-Z0-9 #]{9,28}$/