# File tar.rb, line 223
223:       def read( num=nil )
224:         sanity_checks
225: 
226:         remaining = ( @start + @length ) - @file.pos
227:         num = remaining if num.nil? or num > remaining
228: 
229:         return nil if num < 1
230: 
231:         data = @file.read( num )
232:         @last_pos = @file.pos
233: 
234:         return data
235:       end