#!/usr/bin/perl -w
use strict;

my %foo = (
    camshaft   => 'lumpy',
    gearbox    => 'shifty',
    drivetrain => 'speedy',
    smokestack => 'dirty',
    lights     => 'bright eyes',
);

##</code><code>##

my %bar;
@bar{ qw/camshaft gearbox1 the_drivetrain _other/ } = '';

##</code><code>##

my %map_foo_to_bar = (
    camshaft   => 'camshaft',
    gearbox    => 'gearbox1',
    drivetrain => 'the_drivetrain',
    smokestack => 'my_smokestack',
    junkyard   => '_junkyard',
);

##</code><code>##

sub schlep($$$)
{
    my( $map_ref, $from_ref, $to_ref ) = ( shift, shift, shift );
    for( keys %{ $from_ref } )
    {
        $to_ref->{ $map_ref->{$_} } = $from_ref->{$_}
            if( exists $map_ref->{$_} && exists $to_ref->{ $map_ref->{$_} } )
    }
}

schlep(\%map_foo_to_bar, \%foo, \%bar);

use Data::Dumper;
print Dumper \%bar;