data DateFormats(keep=DateString Informat);
if prxmatch("/\d{4}[\/-]\d{1,2}[\/-]\d{1,2}/",DateString)
/* 4 digits,dash or slash,1-2 digits,dash or slash,1-2 digits */
then Informat="YYMMDD10.";
else if prxmatch("/\d{1,2}[\/-]\d{1,2}[\/-]\d{4}/",DateString)
/* 1-2 digits,dash or slash,1-2 digits,dash or slash,4 digits */
then Informat="MMDDYY10.";
else if prxmatch("/\d{1,2}\w{3}\d{4}/",DateString)
/* 1-2 digits,3 letters,4 digits */
then Informat="DATE9.";
else Informat="unknown";
run;