I wrote a procedure which imports data from an xml-file into a MariaDB using library DBI. The procedure works but I don't understand why the following code gives me the message:
use of uninitialized value $DBI::err in concatenation (.) or string at ...
Here the code (abbreviated):
my $insert_art = $dbh->prepare(
"INSERT INTO odbb_articles (creation_dt,ref_data,comp_no)".
"VALUES (?,?,?)"
);
....
my $comp_no = $xpc->findvalue('./sr:ARTCOMP/sr:COMPNO',$node1);
....
$insert_art->execute($creation_dt,$ref_data,$comp_no)
or die "Fehler bei der Ausfuehrung: ".
"$DBI::err -> $DBI::errstr (odbb_articles $DBI::state)\n";
If I insert the code
if ($comp_no eq "") { $comp_no = undef; }
just before $insert_art->execute the procedure works. This error happens when there is no entry in the xml-file for element COMPNO. I can avoid it if I define it as undef. I just wonder
why $comp_no cause this problem and
is there another solution than to control if $comp_no is "" and define it as undef?
The reason for the second question is to avoid the if statement if there are a lot of variables/columns which may have empty entries.
Thanks for help.
use of uninitialized value $DBI::err in concatenation (.) or string at ...
The error message you are seeing is Perl telling you that $DBI::err is undef. That is not because of the value of your $comp_no. It's just a result of what your program is doing.
So when you pass an empty string to the comp_no column, the database doesn't like that. It throws an error. DBI catches that error and passes it on. The $insert_art->execute returns a false value and the right-hand-side of the or gets called. That's your die.
Now in the string that you pass to die you put three variables:
$DBI::err
$DBI::errstr
$DBI::state
According to the DBI documentation, those are equivalent to the functions $h->err, $h->errstr and $h->state with $h being the last handle used. Let's look at the docs for those.
$h->err
Returns the native database engine error code from the last driver method called. The code is typically an integer but you should not assume that.
The DBI resets $h->err to undef before almost all DBI method calls, so the value only has a short lifespan. Also, for most drivers, the statement handles share the same error variable as the parent database handle, so calling a method on one handle may reset the error on the related handles. [...]
This does not explain when it can be undef.
$h->errstr
Returns the native database engine error message from the last DBI method called. This has the same lifespan issues as the "err" method described above.
The returned string may contain multiple messages separated by newline characters.
The errstr() method should not be used to test for errors, use err() for that, because drivers may return 'success with information' or warning messages via errstr() for methods that have not 'failed'.
Ok, so this is text. Don't use it to test for specific errors. You're not doing that. You just want to give debug output when the program fails.
$h->state
Returns a state code in the standard SQLSTATE five character format. Note that the specific success code 00000 is translated to any empty string (false). If the driver does not support SQLSTATE (and most don't), then state() will return S1000 (General Error) for all errors.
The driver is free to return any value via state, e.g., warning codes, even if it has not declared an error by returning a true value via the "err" method described above.
The state() method should not be used to test for errors, use err() for that, because drivers may return a 'success with information' or warning state code via state() for methods that have not 'failed'.
Again, this is not very clear about how useful it is.
My advice is to get rid of $DBI::err and $DBI::state. You don't need those to figure out what the problem is. Just output $DBI::errstr.
$insert_art->execute($creation_dt,$ref_data,$comp_no)
or die "Fehler bei der Ausfuehrung: " . $dbh->errstr;
Now your program will still fail, but at least you will have a meaningful error message that will explain what your database didn't like about the statement. That's better than being told how there is a bug in your error handling code.
Afterwards, the other answers will probably apply to fix the reason this is happening in the first case.
On another note, a word on die: If you provide a \n at the end of your arguments, it will not print your current script, line number and input handle line number. But those might be useful in your case. You can include them.
In a SQL database an empty string is very different to null.
If comp_no has a foreign key pointing to a record in another table, then the value "" is an accettable one only if there is a record with "" as primary key, very improbable.
Yu can fix this converting empty values to undef:
for ($creation_dt,$ref_data,$comp_no ){
defined $_ and $_ eq '' and $_ = undef;
}
$insert_art->execute($creation_dt,$ref_data,$comp_no);
or also
$insert_art->execute(map {defined($_) && length($_) ? $_ : undef} ($creation_dt,$ref_data,$comp_no));
This is a possible shortcut:
$comp_no ||= undef;
With the caveat that this will work in any case where $comp_no evaluates as false, meaning a value of 0 will actually cause the result to go undef also, which may or may not matter to you. If your field is numeric, I'd say it matters a lot.
Related
I have a monthly Script running to archive files from past month. I'm using Archive::Tar to generate the archive. How can I check if calls to the ->write method are successful?
Does the following work? I didn't manage to fail $tar->write() yet.
unless ($tar->write( $name . '.tar.xz', COMPRESS_XZ )) {
die("cant write tar"); # or any other doings instead
}
Yes, the code in your question will catch any error within ->write.
The documentation of Archive::Tar does not specify what the return value of write is (except when no argument is provided, which isn't the case here). However, looking at the code of the module, write returns undef in case of an error and a true value in case of success:
1 if it was writing to a file (this is the case for the code in your question)
the written string if it was writing in a string.
Note that if something goes wrong and Archive::Tar returns undef, then it will also print an error message (unless you set $Archive::Tar::WARN to 0 by doing $Archive::Tar::WARN = 0). If you want to do something specific depending on the error, you can access the error message using the ->error method.
I have been trying to get perl subroutine value and substitution to get the required part of string from randomips subroutine in exim.conf. However when i use string substitution i get error as follow:
Here is what I am trying to achieve
I am trying to split string by colon and get first occurrence as "interface". I'll be using second occurrence as the "helo_data.
exim.pl
sub randomhosts {
#inet = ("x.x.x.1:hostname1.domain.com","x.x.x.2:hostname2.domain.com","x.x.x.3:hostname3.domain.com"
);
return $inet[int rand($#inet+1)];
}
exim.conf
dkim_remote_smtp:
driver = smtp
interface = "${perl{randomhosts}%:*}"
helo_data = "${sender_address_domain}"
Error I get is as follow:
"failed to expand "interface" option for dkim_remote_smtp transport: missing '}' after 'perl'".
Probably the syntax.
Any help?
The code that you are trying to copy was written by someone who doesn't know much about Perl. It includes this line:
return $inet[int rand($#inet+1)];
A Perl programmer would write this as
return $inet[rand #inet];
I think there are a couple of issues here - one with your Exim syntax and one with your Perl syntax.
Exim is giving you this error:
failed to expand "interface" option for dkim_remote_smtp transport: missing '}' after 'perl'
I don't know anything about calling Perl from Exim, but this page mentions a syntax like ${perl{foo}} (which is similar to the one used in the page you are copying from) and one like ${perl{foo}{argument}} for calling a subroutine and passing it an argument. Nowhere does it mention syntax like yours:
${perl{randomhosts}%:*}
I'm not sure where you have got that syntax from, but it seems likely that this is what is causing your first error.
In a comment, you say
I am stying to get first part of string before colon for each random array value for "interface" and part after colon for "helo_data"
It seems to me that Exim doesn't support this requirement. You would need to call the function twice to get the two pieces of information that you require. You might be able to do this in the Perl using something like state variables - but it would be far more complex than the code you currently have there.
Secondly, your Perl code has a syntax error, so even if Exim was able to call your code, it wouldn't work.
The code you're copying sets up #inet like this:
#inet = ("x.x.x.1", "x.x.x.2", "x.x.x.3", "x.x.x.4");
Your equivalent code is this:
#inet = (
"x.x.x.1:hostname1.domain.com",
"x.x.x.2:hostname2.domain.com,
x.x.x.3:hostname3.domain.com
);
I've reformatted it, to make the problems more obvious. You are missing a number of quote marks around the elements of the array. (Note: I see that while I have been writing this answer, you have fixed that.)
Update: Ok, here is some code to put into exim.pl that does what you want.
use feature qw[state];
sub randomhosts {
state $current;
my #inet = (
"x.x.x.1:hostname1.domain.com",
"x.x.x.2:hostname2.domain.com",
"x.x.x.3:hostname3.domain.com"
);
if ($_[0] eq 'generate') {
shift;
#{$current}{qw[ip host]} = split /:/, $inet[rand #inet];
}
return $current->{$_[0]};
}
It generates a new ip/host pair if its first argument is 'generate'. It will then return either the hostname or the ip address from the generated pair. I think you can probably call it from your Exim config file like this:
dkim_remote_smtp:
driver = smtp
interface = "${perl{randomhosts}{generate}{ip}}"
helo_data = "${perl{randomhosts}{host}}"
But I'm no expert in Exim, so that syntax might need tweaking.
First I would like to note I have not worked with exim so I cannot say what exactly you are trying to do and why you have done things exactly so.
In the link you posted, a method called 'randinet' is added to exim.pl and the interface line in exim.conf is replaced by
interface = "${perl{randinet}}"
You have implemented a 'randomhosts' method and replaced the interface line with
interface = "${perl{randomhosts}%:*}"
Now the parser complains about not finding the closing bracket. That is likely due to the symbols you felt free to add but the parser does not have the freedom to ignore.
I suggest you try
interface = "${perl{randomhosts}}"
In one of my scripts I use the Getopt::Long library. At the beginning of the program I make a call:
&GetOptions ('help', 'debug', 'user=s' => \$GetUser);
The first two arguments are simple: I discover their existance by checking $opt_help and $opt_debug respectively. However the third argument is tricky, because I need to distinguish between no option at all ($GetUser is undefined, which is ok for me), using "--user" alone ($GetUser is also undefined, but this time I want to display an error message) and "--user FooBar" (where the $GetUser receives 'FooBar', which I can use in further processing).
How can I distinguish between using no "--user" option and using it alone, without a username?
You are looking for : instead of =, so 'user:s' => \$GetUser. From Options with values
Using a colon : instead of the equals sign indicates that the option value is optional. In this case, if no suitable value is supplied, string valued options get an empty string '' assigned, while numeric options are set to 0
This allows you to legitimately call the program with --user and no value (with = it's an error). Then you only declare my $GetUser; and after the options are processed you can tell what happened. If it is undef it wasn't mentioned, if it is '' (empty string) it was invoked without a value and you can emit your message. This assumes that it being '' isn't of any other use in your program.
Otherwise, when you use 'user=s' and no value is given, the GetOptions reports an error by returning false and emits a descriptive message to STDERR. So you may well leave it and do
GetOptions( 'user=s' => ...) or die "Option error\n";
and rely on the module to catch and report wrong use. Our own message above isn't really needed as module's messages clearly describe the problem.
One other way of doing this would go along the lines of
usage(), exit if not GetOptions('user=s' => \$GetUser, ...);
sub usage {
# Your usage message, briefly listing options etc.
}
I'd like to add – you don't need & in front of a function call. It makes the caller's #_ visible, ignores function prototype, and does a few other similarly involved things. One common use is to get a coderef, $rc = \&fun, where it is needed. See for example this post
It seems to me that there simply has to be a better way of doing this, but i still haven't found one. And i'm sure i'm not the only one who could use a way to do this: Run an SQL query that only produces one field in one row, then assign that field to a scalar. (In my case, if the query results in more than one field/row, then i have bigger things to worry about than the script breaking).
For example, to get the timestamp from the SQL server, one could use:
my $timestamp;
my $cmd = $dbh->prepare('SELECT cast(now() AS timestamp);') or die $!;
$cmd->execute();
while (my #asd = $cmd->fetchrow_array) { $timestamp = $asd[0] }
Dirty, but it works. But using 4 lines seem a bit much for a simple assignment, especially considering how well perl and postgresql can communicate with eachother via DBI. Sure, i could write a subroutine for it, but isn't there something native that allows me to fetch data as easily as i submit data with $dbh->do() ?
And yes, i did try google.
Usually I write:
$value = $dbh->selectall_arrayref($sql)->[0]->[0];
There's always selectrow_array:
selectrow_array
#row_ary = $dbh->selectrow_array($statement);
#row_ary = $dbh->selectrow_array($statement, \%attr);
#row_ary = $dbh->selectrow_array($statement, \%attr, #bind_values);
This utility method combines prepare, execute and fetchrow_array into a single call.
So something like this:
my $timestamp = $dbh->selectrow_array('select cast(now() as timestamp)');
There's also selectrow_arrayref and selectrow_hashref for similar situations.
From perldoc DBI:
"selectrow_arrayref"
$ary_ref = $dbh->selectrow_arrayref($statement);
$ary_ref = $dbh->selectrow_arrayref($statement, \%attr);
$ary_ref = $dbh->selectrow_arrayref($statement, \%attr, #bind_values);
This utility method combines "prepare", "execute" and
"fetchrow_arrayref" into a single call. It returns the first row of
data from the statement. The $statement parameter can be a previously
prepared statement handle, in which case the "prepare" is skipped.
If any method fails, and "RaiseError" is not set, "selectrow_array"
will return undef.
That will get you most of the way. You still need to do some error checking, but you would be doing that anyway.
Wouldn't fetchrow_array actually only return a scalar as you're only asking for one column?
i am writing a small perl app using the eXist database, and i am wondering is:
how can i see that my call
my $eXist = XML::eXistDB::RPC->new( destination=>$eXist_db, repository=>$bank, user=>"admin", password=>"pass" ) ;
is successful or not ?
thanx
When object initialisation fails, it will be messaged through Log::Report, so hook into that.
This only happens if the programmer to neglected to set either rpc or destination parameter. The new constructor will always return an object instance.
According to the docs:
All methods return a LIST, where the
first scalar is a return code (RC).
When that code is 0, all went well.
Otherwise, the code represent the
transport error or the exception
(refusal) as reported by the server
logic. In either case, the second
scalar in the returned list contains
the error message. For instance,
Maybe this applies also for the constructor, try:
my ($rc,$eXist) = XML::eXistDB::RPC->new( destination=>$eXist_db, repository=>$bank, user=>"admin", password=>"pass" );
now, if $rc != 0 there was an error.