Hi perleager. I didn't mean to sound too harsh, and it's not like indenting is the most important thing and tastes vary. But in a chunk of code like you have, I find it most useful to indent mostly based on blocks -- start the indent with the opening "{" of the block and end the indent with the closing "}". This lets you see at a glance which block each line is part of and also to easily check to make sure you didn't omit a curly brace. I sometimes also indent arguments to functions using the opening and closing parentheses to see where to indent. Here's how I would indent your code (again, tastes vary, this is just my way):

use DBI;

my $dbh = DBI->connect(
    $main::location,
    $main::user,
    $main::ba_pass,
    {RaiseError=>1,AutoCommit=>1}
) or die "Couldn't connect to database: " . $DBI::errstr;

#
# indent one level for the eval block
#
eval {
    my $sth= $dbh->prepare("SELECT id FROM sessions");
    my $id;
    $sth->execute();
    $sth->bind_columns(undef, \$id);
    require CGI::Session;
    import CGI::Session;
    #
    #  indent a second level for the while block
    #
    while ($sth->fetch()) {
        my $session = CGI::Session->load(
            "driver:MySQL", $id, {Handle=>$dbh}
        );
        next if $session->is_empty;
        #
        # indent a third level for the if block
        #
        if (($session->ctime + $session->etime) <= time()) {
            $session->delete();
        }
    }
};
if ($@) {
    print $@;
    $dbh->disconnect();
}
[download]

update:renamed it so I could find it :-)