Use proc contents to list all variables and select it from there.

It is a good answer.
Moreover, it is also curious to know why using summary procedure instead of means procedure? Both are available from SAS/Base. Some people may think they are identical; in fact, not fully the same. According to my experiences, MEANS completely covers SUMMARY, but not true vice versa.In fact, SAS does not even give a direct documentation for SUMMARY but try to use the one for MEANS instead.
JingJu

非常感谢楼上们，人大sas真是好地方

_numeric_很实用