#!/usr/bin/perl -w
use strict;
use Data::Dumper;

my %x = map {;   "prefix_$_" => 1 }    qw(a b c);
my %y = map {    "prefix_"."$_" => 1 } qw(a b c);
my %z = map { ''."prefix_$_" => 1 }    qw(a b c);
print Dumper \%y, \%x, \%z;