SAS does not evaluate the content of %PUT - sas

Question

I use this bit outside of any DATA step.
%let sth = 20191111;
%let sthelse=SUBSTR(INPUT(&sth.,12.),1,4);
%put &sthelse.;
It does not yield '2019', which I would expect but rather
SUBSTR(INPUT(20191111,12.),1,4)
What goes wrong here?

Answer 1

Use the macro function %SUBSTR to extract a portion of its argument. Remember, macro values are only character values (not to be confused with data step character variables and values) and have no explicit numeric value, even when the macro value is comprised of all digits.
%let sth = 20191111;
%let first4 = %substr(&sth,1,4);

Answer 2

You are not understanding how the macro pre-processor works. It is just a text replacement tool. It looks for two trigger character, % and & to see where it needs to do work. You can see both at work in your statement:
%let sthelse=SUBSTR(INPUT(&sth.,12.),1,4);
So the % will trigger the macro processor and it will recognize %let as a macro statement. Then the & trigger will cause it to treat &sth. as a macro variable reference to be replaced. So it replaces that and you end up with this statement.
%let sthelse=SUBSTR(INPUT(20191111,12.),1,4);
Since there are no more macro triggers SAS happily stores that text into the macro variable sthelse.
You also seem confused about how numbers and character strings work. If you write this code:
data x;
x=INPUT("20191111",12.);
run;
You would be asking SAS to convert the string 20191111 into the number 20,191,111. So X would be a numeric variable. So it would have the same effect as if you ran this statement instead.
x=20191111;
Now if you then ask SAS to try to use the SUBSTR() function on that NUMERIC value by doing this:
y=substr(x,1,4);
SAS will need to first convert X into a character string. It will happily do that for you, but it will use the BEST12. format to make the conversion. So your number 20,191,111 will become the string
20191111
So it will have 4 leading spaces. Then if you take the first four characters you end up with four spaces.
Did you intend to run this code instead?
%let sth = 20191111;
%let sthelse=%substr(&sth,1,4);
That will use the MACRO function %SUBSTR() to take the first four characters of the string you have given it. Since you gave it the string 20191111 (to the macro processor everything is a string, no quotes needed) the result will be the string 2019.

Answer 3

SUBSTR is datastep function.
Try to use it into macro function:
%let sth = 20191111;
%let sthelse=%sysfunc(SUBSTR(%sysfunc(INPUTn(&sth.,12.)),1,4));
%put &sthelse.;

Answer 4

There isn't macro function named substr and input, this function is "data step functions". You should use %sysfunc statement. And macro variables stores as text, so you shouldn't use input function on it.
%let sth = 20191111;
%let sthelse=%sysfunc(SUBSTR(&sth.,1,4));
%put &=sthelse.;
STHELSE=2019
UPDATE(thanks #Tom):
There is macro function %substr, so you can use %SUBSTR(&sth.,1,4) instead of %sysfunc(SUBSTR(&sth.,1,4)).