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Hash Odds and Ends

Some operations on hashes aren't obvious if you're new to Perl. Because of the special nature of hashes, a couple of common operations require functions that aren't necessary for scalars and arrays.

Testing for Keys in a Hash

To test to see whether a key exists in a hash, for example, you might be tempted to try the following syntax:

if ( $Hash{keyval} ) {        # WRONG, in this case
    :
}

This example doesn't work for a few reasons. First, this snippet doesn't test to see whether keyval is a key in a hash; it actually tests the value of the keyval key in the hash. Does it work to test if the key is defined, as in the following?

if ( defined $Hash{keyval} ) {    # WRONG, again in this case
    :
}

Again, this example doesn't quite work. ...