G'day mcfarnell,

Welcome to the Monastery.

You've put your code within <code>...</code> tags; which is good. Please do the same for data, program output, and error/warning messages. That way, we can see exactly what you're seeing.

After commenting out line 30, the real output would have been:

Perl MySQL Connect Demo
Connected to the MySQL database.
[download]

I don't know what the real output associated with "500 internal server error" is because you don't show it. This is an important piece of information which you should always provide when asking for help.

From the code you show, you've almost certainly got a problem with the format of $DSN. See the various formats shown for DBD::mysql: connect().

You also have potential problems with one or more of the interpolated, double-quoted strings that you've shown as "***". Passwords in particular often contain special characters: "pass$word", for instance, will evaluate as the literal string 'pass' concatenated with the value of the variable $word.

Thank you, Ken. I responded to hippo's message below with an update.

my $dbh = DBI->connect( $DSN, $username, $mysqlpassword ) or die "$DBI::errstr";

In addition to kcott's advice about string interpolation and DSN construction, I would also not necessarily trust fatalsToBrowser to present the die message to you. While debugging, just print it instead. That way you'll know better what's going on. I assume throughout this that you have no access to the web server error log.

my $dbh = DBI->connect( $DSN, $username, $mysqlpassword );
if ($dbh) {
    say "Connected to the MySQL database.";
} else {
    say "Catastrophe! Connection failure with DSN '$DSN': $DBI::errstr
+";
}
[download]

Try that. You could also decide to print $username and $mysqlpassword on failure. See the Basic Debugging Checklist for more valuable hints.

Thank you both for these ideas. I'm sorry if I'm not including all the information I should - I'll continue to do the best I can. I checked my dbase, tablename, username, and password. They only contain letters or numbers. The password does have a % sign, but when I printed it out it seems to be ok. Would that cause a problem? I also tried all of the formats for the DSN variable as your link suggested. You can see them in my code commented out. None of them changed the output. So here is my updated code:

#!/usr/bin/perlml
 
use cPanelUserConfig;
 
use 5.010;
use strict;
use warnings;
use CGI::Carp qw/fatalsToBrowser/;
 
print "Content-type: text/html\n\n";
 
#B1. Database name, table name, user name, and password
#respectively.  User name and password are case sensitive.
 my $dbase="***";
 my $tablename="***";
 my $username="***";
 my $mysqlpassword="***";
 
#These two should not need modified unless connecting to MySQL on
#a remote server or to a database platform other than MySQL.
 my $hostname="localhost";
 #my $hostname = "localhost:3306";
 #my $hostname = "p3plcpnl1204.prod.phx3.secureserver.net";
 my $databaseserver="mysql";
 
use DBI;
say "Perl MySQL Connect Demo";
# MySQL database configuration
 
#my $DSN = "dbi:mysql:$dbase:$hostname";
#my $DSN = "DBI:mysql:$dbase";
#my $DSN = "DBI:mysql:database=$dbase;host=$hostname";
my $DSN = "DBI:mysql:database=$dbase;host=$hostname";
 
my $dbh = DBI->connect( $DSN, $username, $mysqlpassword );
my $dbh = "";
if ($dbh) {
    say "Connected to the MySQL database.";
} else {
    say "Catastrophe! Connection failure with DSN '$DSN', pass '$mysql
+password', user '$username': $DBI::errstr
+";
}
[download]

When I run this code as is, the output is:

500 Internal Server Error
Please forward this error screen to cowlitzcountycemeterydistrict6.inf
+o's WebMaster.
The request was not completed. The server met an unexpected condition.

cowlitzcountycemeterydistrict6.info/cgi/test2.pl (port 80)
[download]

When I comment out the DBI->connect line, line number 35, the output is:

Perl MySQL Connect Demo Catastrophe! Connection failure with DSN 'DBI:
+mysql:database=***;host=localhost', pass '***', user '***': +
[download]

I was able to find an error log under cpanel, even though GoDaddy told me I only had access to PHP error logs. The error I am seeing is:

/usr/bin/perlml: relocation error: /home/b3mtw1376jad/perl5/lib/perl5/
+x86_64-linux-thread-multi/auto/DBD/mysql/mysql.so: symbol mysql_optio
+ns4, version libmysqlclient_18 not defined in file libmysqlclient.so.
+18 with link time reference
[download]

I assume this error in the error log is the answer to my problems? But I'm not sure how to fix it. We are on a shared hosting plan. Does this mean I need the server admin to do something? I found this article related to this issue: https://dev.mysql.com/doc/refman/8.0/en/perl-support-problems.html

I was able to find an error log under cpanel, even though GoDaddy told me I only had access to PHP error logs. The error I am seeing is:

/usr/bin/perlml: relocation error: /home/b3mtw1376jad/perl5/lib/perl5/
+x86_64-linux-thread-multi/auto/DBD/mysql/mysql.so: symbol mysql_optio
+ns4, version libmysqlclient_18 not defined in file libmysqlclient.so.
+18 with link time reference
[download]

I assume this error in the error log is the answer to my problems?

Almost certainly it is, yes: at the point of loading the DBD::mysql shared library, it is giving an error that one of the symbols it expects to see in the additional libraries it links to has not been found.

I suspect this means that when the server admin built DBD::mysql they built it against a different version of the mysql libraries than are currently on this server. That is something the server admin will need to fix, and not something you will be able to fix or work around yourself (to the best of my knowledge).

Hopefully contacting them with that error message should be sufficient for them to diagnose and fix the issue.

"The password does have a % sign, but when I printed it out it seems to be ok. Would that cause a problem?"

This is a situation where I would apply "the first great virtue of a programmer": laziness.

Instead of checking if individual strings might be a problem when interpolated; e.g.

$ perl -Mstrict -Mwarnings -E 'my $v = qq{$s@a%h}; say $v'
Possible unintended interpolation of @a in string at -e line 1.
Global symbol "$s" requires explicit package name (did you forget to d
+eclare "my $s"?) at -e line 1.
Global symbol "@a" requires explicit package name (did you forget to d
+eclare "my @a"?) at -e line 1.
Execution of -e aborted due to compilation errors.
[download]

Simply side-step the issue by not interpolating; e.g.

$ perl -Mstrict -Mwarnings -E 'my $v = q{$s@a%h}; say $v'
$s@a%h
[download]

See also: "perlop: Quote and Quote-like Operators"; which starts with a table showing what does, and does not, interpolate.

— Ken