Your
$baseStream
variable is including the newline character(s). Try this:
print "Enter the name";
$baseStream = <> ;
chomp $baseStream;
$b = 1;
$strName = "${baseStream}_Strm_${b}";
print $strName;
"chomp" is a function that removes the line separator from the end of a string.
I've removed the extra $ symbol from inside "{}" too.