I'd also recommend Tie::File or a database.

However, if you really prefer to use a flat file you could try somehing like the following. It selects a random line in the file and does an in-place edit so that the line is effectively removed.

    #!/usr/bin/perl -w

    use strict;

    my $passwords = 'passwords';

    # It would be better to cache the $count value in a separate file
    my $count = `wc -l $passwords`;

    # Bail out if wc failed
    exit if $?;

    # Get the line count
    $count = (split ' ', $count)[0];

    # Bail out if the file is empty
    die "No passwords in $passwords\n" unless $count;


    my $key = 1 + int rand $count;
    my $password;

    # Localised in-place edit
    {
        local $^I = '';
        local @ARGV = $passwords;

        while (<>) {
            if ($. == $key) {
                chomp;
                $password = $_;
            } else {
                print;
            }
        }
    }

    print $password, "\n";

    __END__
[download]

However, if the selection doesn't have to be random it would be more efficient to read a record from the end and then truncate the file as shown below.

--
John.