Try it an see.
filename junk temp;
data _null_;
file junk;
do len=10 to 0 by -1;
x='12345678901234567890';
put x $varying10. len ;
end;
run;
data _null_;
infile junk length=fred;
input;
put _n_= fred= @20 _infile_;
run;
_N_=1 fred=10 1234567890
_N_=2 fred=9 123456789
_N_=3 fred=8 12345678
_N_=4 fred=7 1234567
_N_=5 fred=6 123456
_N_=6 fred=5 12345
_N_=7 fred=4 1234
_N_=8 fred=3 123
_N_=9 fred=2 12
_N_=10 fred=1 1
_N_=11 fred=0
NOTE: 11 records were read from the infile JUNK.
The minimum record length was 0.
The maximum record length was 10.