Using Perl and MySQL

Posted on 2002-06-03
Last Modified: 2010-03-05
I have written Perl code to access a MySQL database.  I am changing the code to cache previously loaded web pages into a 4k text buffer in the database.  The internet response is loaded into a variable called $response as follows:
  $req=HTTP::Request->new("GET", $url);

To save the information the following is done:
  $respstr = $response->as_string;
  $respstr1 = substr($respstr, 0, 4000);
  $cachepage = $respstr1;
  $sql = "update links set cachepage='$cachepage' where id=$id";
  $tda = $dbh->prepare($sql) or die "Error preparing: ", $dbh->errstr;
  $tda->execute or die "Error executing: ", $dbh->errstr;

The variable $cachepage is a text type in the MySQL database.  

When the execute is attempted, no response is returned and I am sure it fails since the database is not written to.
Do I need to set a length work or something to get this to work?  Thanks for any help.
Question by:mzehner
  • 3
  • 2
  • 2

Expert Comment

ID: 7051898
$tda->execute or die "Error executing: ", $dbh->errstr;
$dbh->commit; ## <- you need to commit the update.

Author Comment

ID: 7052391
It still does not work even with $dbh->commit;.  There is no error message, but unless the line:
$tda->execute or die "Error executing: ", $dbh->errstr;
is commented out the web page will not return output.

Expert Comment

ID: 7052444
Silly question...but are you connecting to the DB first?

You also should escape the single quotes

$sql = "update links set cachepage=\'$cachepage\' where id=$id";

I'm pretty sure this is the case...I did a project with MySQL once so this is from memory, also I don't have immediate access to some tools such as perl... In any case, it won't hurt....

One other thing, you shouldn't need to prepare that update statement. Just do:

$sql = "update links set cachepage=\'$cachepage\' where id=$id";
if($DBI::err != 0) {
  print "error here!\n";
  print $dbh->errstr;

Maybe something in there will move you in the right direction...
Do You Know the 4 Main Threat Actor Types?

Do you know the main threat actor types? Most attackers fall into one of four categories, each with their own favored tactics, techniques, and procedures.


Expert Comment

ID: 7053203
Also add this to your script:

use CGI::Carp qw(fatalsToBrowser);

It will cause 'die' messages to go to your browser.

Author Comment

ID: 7058046
I am connecting to the database first since I am performing successful queries prior to the code I posted above.

I tried your suggestion.  It worked with an interesting error.  I stated that I have an error in my SQL syntax near 'Gave information here'.
The interesting thing about the information is that it is part of the string that I am writing to the database.  This is why I suspect that it is a possible problem with the syntax of the variable being written.  I have not used blob or text types (beyond 255 characters) with MySQL before.

I removed:
$respstr = $response->as_string;
and the program worked responded with the text output I placed at the end of it.  It appeared to work, but I'm not sure the datbase contains the web page contents.

Therefore part of the problem was that I was converting it to a string before saving to the database.  I'm not sure why this caused a problem.  I still need to investigate to tell if the data was wriiten to the database.  It does not appear in MySQL admin.

Accepted Solution

dda earned 100 total points
ID: 7058750
I bet you have single or souble quotes in yout text being inserted into database. You can mask them with '\' or, better way, use placeholders and parameters to execute():

$sql = "update links set cachepage=? where id=?";
$tda = $dbh->prepare($sql) or die "Error preparing: ", $dbh->errstr;
$tda->execute($cachepage, $id) or die "Error executing: ", $dbh->errstr;

Author Comment

ID: 7065892
Thanks, your comments helped me debug and solve the problem.

Featured Post

How to improve team productivity

Quip adds documents, spreadsheets, and tasklists to your Slack experience
- Elevate ideas to Quip docs
- Share Quip docs in Slack
- Get notified of changes to your docs
- Available on iOS/Android/Desktop/Web
- Online/Offline

Join & Write a Comment

Suggested Solutions

Title # Comments Views Activity
Strange perl issue 6 122
Perl script to parse xml file 2 96
Writing a parser for java language 4 61
Perl string filter 5 63
In the distant past (last year) I hacked together a little toy that would allow a couple of Manager types to query, preview, and extract data from a number of MongoDB instances, to their tool of choice: Excel (…
Checking the Alert Log in AWS RDS Oracle can be a pain through their user interface.  I made a script to download the Alert Log, look for errors, and email me the trace files.  In this article I'll describe what I did and share my script.
Explain concepts important to validation of email addresses with regular expressions. Applies to most languages/tools that uses regular expressions. Consider email address RFCs: Look at HTML5 form input element (with type=email) regex pattern: T…
Here's a very brief overview of the methods PRTG Network Monitor ( offers for monitoring bandwidth, to help you decide which methods you´d like to investigate in more detail.  The methods are covered in more detail in o…

708 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

15 Experts available now in Live!

Get 1:1 Help Now