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perlfunc:keys

by gods
on Aug 24, 1999 at 22:42 UTC ( #218=perlfunc: print w/replies, xml ) Need Help??

keys

See the current Perl documentation for keys.

Here is our local, out-dated (pre-5.6) version:


keys - retrieve list of indices from a hash



keys HASH



Returns a list consisting of all the keys of the named hash. (In a scalar context, returns the number of keys.) The keys are returned in an apparently random order, but it is the same order as either the values() or each() function produces (given that the hash has not been modified). As a side effect, it resets HASH's iterator.

Here is yet another way to print your environment:

    @keys = keys %ENV;
    @values = values %ENV;
    while ($#keys >= 0) {
        print pop(@keys), '=', pop(@values), "\n";
    }

or how about sorted by key:

    foreach $key (sort(keys %ENV)) {
        print $key, '=', $ENV{$key}, "\n";
    }

To sort an array by value, you'll need to use a sort() function. Here's a descending numeric sort of a hash by its values:

    foreach $key (sort { $hash{$b} <=> $hash{$a} } keys %hash) {
        printf "%4d %s\n", $hash{$key}, $key;
    }

As an lvalue keys() allows you to increase the number of hash buckets allocated for the given hash. This can gain you a measure of efficiency if you know the hash is going to get big. (This is similar to pre-extending an array by assigning a larger number to $#array.) If you say

    keys %hash = 200;

then %hash will have at least 200 buckets allocated for it--256 of them, in fact, since it rounds up to the next power of two. These buckets will be retained even if you do %hash = (), use undef %hash if you want to free the storage while %hash is still in scope. You can't shrink the number of buckets allocated for the hash using keys() in this way (but you needn't worry about doing this by accident, as trying has no effect).


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[ambrus]: Corion: I think I parsed a HTTP header from a string with LWP once. You can definitely use that to create a HTTP message too. The problme is
[ambrus]: that if you do that, you'd have to find where each HTTP response ends, which is nontrivial if you want persistent connections (essential for performance if you have small requests).
[Corion]: ambrus: Yes, ideally an API that I feed the incoming data piece by piece and that I can ask "is that response done" and "what should I do next" and "please construct the appropriate redirect for me"
[Corion]: ambrus: Yes, ideally the module would do all that nasty stuff for me and give me a way to ask it what the current situation is
[ambrus]: Corion: you could also consider using some wrapper over the multi interface of curl, I think Net::Curl might be a good one, since implementing enough of what it expects from the event loop might be easier than a full AnyEvent interface.
[ambrus]: Corion: you could also consider using IO::Async and its POE driver and some HTTP module for it, but I don't know if that would solve your problems with AnyEvent+POE
[ambrus]: Corion: wait, you didn't say POE. You said Prima, let me look up what that is.
[ambrus]: Corion: have you considered just writing an AnyEvent integration for that thing?
[ambrus]: Or perhaps pushing schmorp to write one?
[ambrus]: Also, searching for an existing one on CPAN obviously

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