sub foo {
    my $calling_sub = (caller 1)[3];
    $calling_sub = 'the main block' if !defined $calling_sub;
    print "called from: $calling_sub\n";
}

sub bar {
    foo();
}

bar();  # prints: called from: main::bar
foo();  # prints: called from: the main block

##</code><code>##

# using Sys::Syslog log levels
sub open_db {
    my $dbname = shift;
    # ...
    if (defined $dbh) {
        log_this(LOG_NOTICE, 'OPEN_DB', $dbname, 'db connection established');
    }
    else {
        log_this(LOG_ERR, 'OPEN_DB_NOK', $dbname, 'db connection failed');
    }
}