How to check whether a hash is empty (has no keys)?

[ambrus]

How to check whether a hash is empty (has no keys)?

Originally posted as a Categorized Question.

[ambrus]

Just use the name of the hash in scalar context, such as

if (%foo) {
    # %foo has at least one key
} else {
    # %foo has no keys
}

If you want to be very explicit, you can also write

if (!!%foo) { ... }

or

if (scalar %foo) { ... }

or

if (0+%foo) { ... }

[davido]

keys, in scalar context returns the number of keys in the hash.

if( keys %hash ) {
    # There are keys
} else {
    # There are no keys
}