Difference between defining SAS macrovariables via %let and call symput?

Question

I am not sure what the difference is between

%let m=product and cal symput('m', 'product') is?

Aren't both expressions creating af macrovariable, m, which has the value product?

Answer 1

%let is used to define a macro variable based on text or an expression that resolves to text. It is called in open code, or in a macro. %let automatically trims the macro variable of both leading and trailing blanks. Documentation can be found here.

call symput (documentation here) is used to assign the contents of a SAS dataset variable, an expression that resolves to a SAS dataset variable (or a PDV variable), a character value, or an expression that resolves to a character value (including a numeric value, which resolves to its character equivalent in the default format, normally BEST12.). call symput does not trim leading or trailing blanks, so for example the expression

%let x=5;
%put [&x];

gives you a somewhat different result than the expression

data _null_;
call symput('y',5);
run;
%put [&y];

call symputx (available since 9.2) has more similar results to %let, in that it trims leading and trailing blanks. That is particularly helpful for macro variables created from numbers, as those typically have several leading blanks, like in the above example.

%let and call symput\symputx also have some differences in scoping. Both when used in open code (or a data step not in a macro) will place the macro variable in the global table, but %let used in a macro will place the variable in the most local table that it exists already, if it does; ie, if you have a global variable &myvar then %let myvar=5; will modify the global variable &myvar, not create a locally scoped variable. call symput will place the variable in the most local nonempty symbol table, regardless of whether it exists in a global scope already or not. call symputx will do the same, unless you specify an optional argument indicating which table you wish it to be placed.