Reading the config file seems very straight forward.

my %name_for;
while (<>) {
    my ($name, @aliases) = split;
    $name_for{$_}=$name for ($name,@aliases);
}
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After that, you can take a string of names/aliases and replace them with their real names like so:

my $foo = 'alias1:blah1';
$foo =~ s/(\w+)/$name_for{$1}/g;
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That's assuming quite a few things about the format of $foo, however.

The key to your problem is an appreciation of the power of hashes in Perl. In C++ you may occasionally have used a hash map to allow using a non-integer value to lookup a value in an "associative array". In Perl hashes (hash maps/associative arrays) are fundamental to almost all significant projects. Perl hasn't the richness of types available in C++, but the few that are provided by Perl make up and more in their intrinsic power and richness of operations. Have a good read of perldata, perlref and perllol to get a feel for what can be done.