if ($b=~/^[1-5]\z/) {
   print "\$b has to be a number and is either 1, 2, 3, 4, or 5.\n";
}

##</code><code>##

my $b = "     5    ";

##</code><code>##

my $b = "   \t\t  1  \t  ";

##</code><code>##

$b =~ s/\s+//g; #additional code
if ($b=~/^[1-5]\z/) {
   print "\$b has to be a number and is either 1, 2, 3, 4, or 5.\n";
}