Programming Perl, 4th Edition

each

each HASH
each ARRAY
each EXPR

This function steps through a hash one key/value pair at a time. When called in list context, each returns a two-element list consisting of the key and value for the next element of a hash so that you can iterate over it. When called in scalar context, each returns just the key for the next element in the hash. When the hash is entirely read, the empty list is returned, which when assigned produces a false value in scalar context, such as a loop test. The next call to each after that will start iterating again. The typical use is as follows, using predefined %ENV hash:

while (($key,$value) = each %ENV) {
    say "$key=$value";
}

Internally, a hash maintains its own entries in an apparently random order. The each function iterates through this sequence because every hash remembers which entry was last returned. The actual ordering of this sequence is subject to change in future versions of Perl, but is guaranteed to be in the same order as the keys (or values) function would produce on the same (unmodified) hash. For security reasons, this ordering can vary between different runs of the same program.

Perl maintains a single iterator for each hash, shared by all each, keys, and values function calls in the program; it can be reset by reading all the elements from the hash, or by evaluating keys %hash or values %hash. If you add or delete elements of a hash ...