#!/usr/local/bin/perl -w

use strict;

my $ref={ a => 'aa', b => 'bb'};

print "The hash, before:$/";
print %$ref;

print qq($/The hash "during":$/);
for (%$ref) {
    /[A-Z]/ or $_ = 'x';
    print;
}

print "$/The hash, after:$/";
print %$ref;
print $/;
__END__
The hash, before:
aaabbb
The hash "during":
xxxx
The hash, after:
axbx