#!/usr/bin/perl -w

my $str = "abcdefg";

my %hash;

%hash = map {$_ => $_} split //, $str;

print qq{$_ => $hash{$_}\n} for sort keys %hash;
[download]

When run:

# ./t.pl
a => a
b => b
c => c
d => d
e => e
f => f
g => g
[download]

Cheers,
KM