Expand hostnames from a string of hostnames and/or regex

Question

This code will be passed a string which will contain one or more hostnames.

A hostname can be

• dotted-decimal
• plain name (like my_host)
• FQDN or even partially qualified
• A string containing regex (my_hos[tes])

target_list is an array of known hosts to match any regex against.

Any suggestions on cleaning this up?

sub expand_names {
 my $host = shift;
 my @raw_hosts = split(' ', $host);
 my @hosts;
 my %host_hash;
 foreach my $raw_name (@raw_hosts) {
 $host_hash{$raw_name} = {};
 #if the name might contain regex, let's see what it matched
 if ($raw_name !~ m/^[a-zA-Z0-9-]+$/) {
 foreach my $target (@target_list) {
 if ($target =~ m/^$raw_name$/) {
 $host_hash{$raw_name}->{$target} = 1;
 }
 }
 #if we didn't match anything, then just use the name
 if (not keys %{$host_hash{$raw_name}} ) {
 $host_hash{$raw_name}->{$raw_name} = 1;
 }
 }
 else {
 # Regular host name or dotted-decimal
 $host_hash{$raw_name}->{$raw_name} = 1;
 }
 }
 # Gather all the hosts we found
 foreach $raw_name (keys %host_hash) {
 @hosts = (@hosts, (keys %{$host_hash{$raw_name}}));
 }
 return sort @hosts;
}

Answer 1

Your function expects a single argument that should contain hostnames or patterns separated by spaces:

sub expand_names {
 my $host = shift;
 my @raw_hosts = split(' ', $host);
 foreach my $raw_name (@raw_hosts) {

Why not use multiple arguments?

sub expand_names {
 foreach my $raw_name (@_) {

Since @hosts is empty when you reach this code:

# Gather all the hosts we found
foreach $raw_name (keys %host_hash) {
 @hosts = (@hosts, (keys %{$host_hash{$raw_name}}));
}

You could simplify:

foreach $raw_name (keys %host_hash) {
 push(@hosts, keys %{$host_hash{$raw_name}});
}

And actually, I don't see the reason for building a map of maps, when a simple flat map will do. Consider this alternative implementation:

sub expand_names {
 my %hosts;
 foreach my $raw_name (@_) {
 #if the name might contain regex, let's see what it matched
 if ($raw_name !~ m/^[a-zA-Z0-9-]+$/) {
 my $found = 0;
 foreach my $target (@target_list) {
 if ($target =~ m/^$raw_name$/) {
 $found = $hosts{$target} = 1;
 }
 }
 $hosts{$raw_name} = 1 if not $found;
 } else {
 # Regular host name or dotted-decimal
 $hosts{$raw_name} = 1;
 }
 }
 return sort keys %hosts;
}