Question

Why does this statement,

    if (! $ssh_options{user}) {

    delete $ssh_options{user};

}

return true, but this statement

    if ($ssh_options{user} eq 'undef') {

    delete $ssh_options{user};

}

give me the error,

Use of uninitialized value $ssh_options{"user"} in string eq at analyze.pl line 230.

I thought you always had to have something for perl to compare the value of the variable being compared.

** Update **

@ Quick Joe Smith

I cannot base my comparison on whether the hash keys exist or not because the values for this hash

sub ssh_connect {

my $host = shift;

my %ssh_options = (

    port => shift,
    user => shift,
    password => shift

    );

Come from this function which calls the sub routine

        if ((exists $config_file{user}) && (exists $config_file{password})) {

        my $vmware_user = $config_file{user};

        my $vmware_password = $config_file{password};

        ssh_connect($vmware_host, $vmware_port, $vmware_user, $vmware_password);

    } else {

        ssh_connect($vmware_host, $vmware_port);

    }

Answer 1

Perl hash slots have a number of ways they can be false. If the key has never been filled, the exists function will return false. If the key exists but contains an undefined value, exists will be true but the defined function will return false. In normal boolean context, as given by an if statement, a hash key that was never filled, or is undefined, '', 0 or anything that reduces to those will be false.

From your update, it sounds like what you want is to use defined

delete $ssh_options{user} unless defined $ssh_options{user};