How is the username field defined?

It works fine unless username isn't found, and then I just get an error message:

If the username isn't found, then the statement is being executed successfully and the die statement won't be called. If it is being called, then the statement is failing.

The first step I'd take would be to verify the contents of $contents{'username'} to make sure it contains EXACTLY what you expect. Then run the sql statement from the mysql cli to see if it succeeds or fails with an error message.

Wait, I might be wrong on one point. I need to run a test but I think an empty list will return false in scalar context. If so, that would be the reason why the die statement is being executed.

The first step I'd take would be to verify the contents of $contents{'username'} to make sure it contains EXACTLY what you expect.

I test for the minimum requirements: that it contains at least 1 letter, and then trim any opening or trailing spaces. But in my testing, I'm getting the error on simple mistakes; eg, the registered username is "csdude55" and the user typed "csdude5" (which doesn't exist).

I need to run a test but I think an empty list will return false in scalar context. If so, that would be the reason why the die statement is being executed.

The docs referred to context sensitivity, too, so you're right on that point:

If called in a list context, 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 an empty list.

If called in a scalar context for a statement handle that has more than one column, it is undefined whether the driver will return the value of the first column or the last. So don't do that.

I had never really heard of "context sensitivity" in Perl before, and the docs don't clarify it at all. But if I understand correctly, I'm assigning it to a list, right?

($found_password, $found_email) = ...;

If I'm wrong, what's the right way to assign it to a list? Or SHOULD I be assigning it to a scalar?

That is the correct way to assign a list. What I'm not sure about (since my perl is a bit rusty) is what DBI is using when when testing the or conditional portion of the statement.

You could take the or die statement out and instead $dbh->errstr or the $found_password and $found_email vars.

Personally, I normally don't like doing db handle calls like that. I prefer to separate out the prepare and execute statements so that I can have finer granularity on the error handling.

Off topic: Doesn't this forum allow us to edit our posts to fix typos? Or do I need to have some minimum number of posts before that access right is given?

[edited by: fishmonger at 7:36 pm (utc) on Jun 22, 2019]

OT response - Editing can be done for a short time after posting. Beyond that initial limit you can report the error and request a correction. To do that, click on the Msg# button.

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;)

Great, ty

if ($contents{'username'}) {
 ($found_password, $found_email) =
 $dbh->selectrow_array("SELECT password, email FROM users WHERE username=? LIMIT 1", undef,
 $contents{'username'}) or die "Couldn't execute SELECT FROM users: " . $dbh->errstr;
}

If the username isn't found, then the statement is being executed successfully and the die statement won't be called. If it is being called, then the statement is failing.

That is the correct way to assign a list. What I'm not sure about (since my perl is a bit rusty) is what DBI is using when when testing the or conditional portion of the statement.

the basic code structure here is:
if(something){assignment or die}

DBI has nothing to do with the conditional.
it's only the perl assignment that is involved.
in a perl assignment operation, "the final value of the variable on the left is returned as the value of the assignment as a whole" [oreilly.com] (quoted from the "camel book")

So, when that DBI call doesn't find the username, it returns an empty list which evaluates to false and triggers the or die clause to execute.

There are a couple ways to correct this problem. One would be to remove the or die clause and use a separate statement to test the success/failure of retrieving the data.

remove the or die clause and use a separate statement to test the success/failure of retrieving the data

that's where i would start.

Ha! You guys are right... I removed the or die clause, and now it works just fine.

I would have never guessed that one.