各位大侠帮帮忙，能否帮我解释一下这段程序，这个问题也许很幼稚，见笑了。

PROC CATALOG CATALOG=<libref.>catalog <ENTRYTYPE=etype> <FORCE>
<KILL>;
CONTENTS <OUT=SAS-data-set> <FILE=fileref>;
COPY OUT=<libref.>catalog <options>;
SELECT entry(s) </ ENTRYTYPE=etype>;
EXCLUDE entry(s) </ ENTRYTYPE=etype>;
CHANGE old-name-1=new-name-1
<…old-name-n=new-name-n>
</ ENTRYTYPE=etype>;
EXCHANGE name-1=other-name-1
<…name-n=other-name-n>
</ ENTRYTYPE=etype>;
DELETE entry(s) </ ENTRYTYPE=etype>;
MODIFY entry (DESCRIPTION=<<’>entry-description<’>>)</ ENTRYTYPE=etype>;
SAVE entry(s) </ ENTRYTYPE=etype>;

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