#! perl -slw
use strict;

( $a, $b ) = ( 'mya', 'myb' );
# imagine several lines of intervening code
{
    our( $a, $b ) = ( 'oura', 'ourb' );
    my @sorted = sort { $a <=> $b } map{ rand 100 } 0 .. 99;
    print "$a : $b";
}
print "$a : $b";
__END__
C:\s>perl sortab.pl
oura : ourb
oura : ourb #no warnings, $a and $b are quietly changed