feat: mf_existfileref macro

base/mf_existfileref.sas

@@ -0,0 +1,31 @@
+/**
+  @file
+  @brief Checks whether a fileref exists
+  @details You can probably do without this macro as it is just a one liner.
+  Mainly it is here as a convenient way to remember the syntax!
+
+  For this macro, if the fileref exists but the underlying file does not exist
+
+  @param fref the fileref to detect
+
+  @return output returns 1 if found AND the file exists.  0 is returned if not
+  found, and -1 is returned if the fileref is found but the file does not exist.
+
+  @version 8
+  @author [Allan Bowe](https://www.linkedin.com/in/allanbowe/)
+**/
+
+%macro mf_existfileref(fref
+)/*/STORE SOURCE*/;
+  %local result;
+  %let result=%sysfunc(fileref(&fref));
+  %if  &result>0 %then %do;
+    0
+  %end;
+  %else %if &result=0 %then %do;
+    1
+  %end;
+  %else %do;
+    -1
+  %end;
+%mend;