Need a hand with rebuilding hashes out of a db.

swares has asked for the wisdom of the Perl Monks concerning the following question:

I am reading in data from a db trying to reconstruct a hash which has a hash reference in it. What I'm getting is a hash with an anonymous hash in it rather than a hash reference, I believe.


How do I get the right data structure?

Here is what the data looks like printed:
-- What I Get (BAD) --
[print_rnd_line](^!rob),swares,swares!chatzilla@pendulum-A127A504.wecm
+.ibm.com,ARRAY(0x9a9e090),#bots2,{
        'file' => '/home/issuebot/data/rob.txt',
},!rob
-- What I Need (GOOD) --
[print_rnd_line](^!rob),swares,swares!chatzilla@pendulum-A127A504.wecm
+.ibm.com,ARRAY(0x9ab13c8),#bots2,HASH(0x9a4ad0c),!rob
[Hal] Got Text [!rob]

Here is a code snippet of the offending code:
    while ((@row) = $sth->fetchrow_array) {
        $line= join(";", map {defined $_ ? $_ : "(null)"} @row);
        ($id, $name, $command, $reply_to, $listen_on, $requires, $help
+, $description, $sub_name, $args, $sub_code, $whenactive, $enabled, $
+subscribed)=split /;/,$line;
        print "[load_plugins] Config $id, $name, $command, $reply_to, 
+$listen_on, $requires, $help, $description, $sub_name, $args, $sub_co
+de, $whenactive, $enabled, $subscribed\n";
        # subscriber handler
        my (@subscribed) = split /[\s|\n]+/, $subscribed;
        foreach my $subscrber (@subscribed){
            if ($subscrber =~ /$identity_id/){$subscribed="true";last}
+;
        }
        if ($subscribed !~ /true/){next};
        if ($enabled =~ /true/){

# fix $args hash ref
# $args needs to be a reference

        $public_handlers{"$name"} = (
                {    id => $id,
                    name => "$name",
                    command => "$command",
                    reply_to => "$reply_to",
                    listen_on => "$listen_on",
                    requires => "$requires",
                    help => "$help",
                    description => "$description",
                    sub => "$sub_name",
                    args => "$args",
                    sub_code => "$sub_code",
                    whenactive => "$whenactive",
                    enabled => "$enabled",
                },
            );
[download]

Comment on Need a hand with rebuilding hashes out of a db. Download Code

Replies are listed 'Best First'.

Re: Need a hand with rebuilding hashes out of a db.
by Jenda (Abbot) on Apr 04, 2007 at 09:17 UTC

THIS IS NOT A SHELL SCRIPT! DON'T ENCLOSE VARIABLES IN DOUBLEQUOTES!

Sorry for screaming, but foo( "$varname") or $hash{"$varname"} is a sure sign you misunderstood something. And you are begging for problems. If the variable contains a number, then by enclosing it in double quotes you force perl to convert it to a string and make a copy of that string. If it's already a string you only make a copy. Just a waste, BUT if it's a reference you kill the reference. The thing you end up with will no longer be a reference. It will be just a string that will look a bit as if it was a reference but it will not work:

my %h = (a => 5, b => 9);
my $ref = \%h;
print "\$ref->{a}=$ref->{a}\n";

my $not_ref = "$ref";
print "\$not_ref->{a}=$not_ref->{a}\n";

print "Even though $ref == $not_ref\n";
[download]

While there are valid reasons to force stringification to a variable, they are very very rare! So please drop all your doublequotes around your variables!

Update: Anno is right, $ref == $not_ref evaluates to false, $ref eq $not_ref would evaluate to true. I meant

print "Even though $ref looks like $not_ref\n";
[download]

Jenda
Support Denmark!
Defend the free world!

[reply]
[d/l]
[select]

Re^2: Need a hand with rebuilding hashes out of a db.

by Anno (Deacon) on Apr 04, 2007 at 10:09 UTC

print "Even though $ref eq $not_ref\n";
[download]

[reply]
[d/l]