Find key name in hash with only one key?

Question

If I have a hash

my %h = (
    secret => 1;
);

and I know that is only is one key in the hash, but I don't know what it is called.

Do I then have to iterate through that hash

my $key;
foreach my $i (keys %h) {
    $key = $h{$i};
}

Or are there a better way to get the name of the key?

Solution 1

A list slice should do it

(keys %h)[0]

keys returns a list, so just extract the first element of that list.

Solution 2

my ($key) = keys %h;

As you're using list context on both sides of the assignment operator, the first item in the keys list gets assigned to $key.

Solution 3

I do not believe it is necessary to use the keys function.

my ($key) = %h;

or

my $key = (%h)[0];

The hash inside the parens will be expanded to a list, then we can simply take the first element of that list, which is the key.

Solution 4

my @keys = keys %h;
my $key = $keys[0];

Solution 5

[ keys %h ]->[0] will also do the disambiguation Joel mentions in an earlier comment. This code smells like it will cause problems though. If there is really only a single key/value pair, there might be a better way to handle the data.

At the least, I'd check to be sure the expectation is never violated silently. E.g.‐

keys %h == 1 or die "ETOOMANYKEYS";
print [ keys %h ]->[0], $/;

View more solutions