I want to restrict the scope of number.

It's not clear to me, but it seems possible you're actually asking "I want to restrict the scope of the $number scalar." If that's the case, then one way is to establish an independent scope  { ... } for the variable:

c:\@Work\Perl\monks>perl -wMstrict -le
"my $number = 42;
 print '$number before independent scope == ', $number;
 ;;
 { my $number = 8;
   print '$number in independent scope == ', $number++ for 1 .. 5;
   }
 ;;
 print '$number after independent scope == ', $number;
"
$number before independent scope == 42
$number in independent scope == 8
$number in independent scope == 9
$number in independent scope == 10
$number in independent scope == 11
$number in independent scope == 12
$number after independent scope == 42
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Update: Discussions of scoping can be found throughout perlsyn and among the Tutorials in the Variables and Scoping section.