dir命令读取全部文件，然后再传给程序处理；
dir List directory.
DIR directory_name lists the files in a directory. Pathnames and
wildcards may be used. For example, DIR *.m lists all the M-files
in the current directory.
D = DIR(directory_name) returns the results in an M-by-1
structure with the fields:
name — filename
date — modification date
bytes — number of bytes allocated to the file
isdir — 1 if name is a directory and 0 if not
