Proc Summary defaults to NOPRINT Proc MEANS defaults to PRINT
If you omit the VAR statement, then PROC SUMMARY PRODUCES a simple count of observations, whereas PROC MEANS tries to ANALYZE all the numeric variables that are not listed in the other statements
If you specify statistics on the PROC SUMMARY statement and the VAR statement is OMITTED, then PROC SUMMARY stops processing and an error message is written to the SAS LOG.
If you omit the VAR statement, then PROC MEANS analyzes all numeric variables that are not listed in the other statements. When all variables are character variables, PROC MEANS produces a simple count of observations.