Why Does My PHP Script Fail to Connect to MySQL When the Password Contains a Dollar Sign?

Dollar ($) Sign in Password String Misinterpreted as Variable

When encountering connection issues with a PHP/MySQL web application despite successful database access with identical credentials through the shell and phpMyAdmin, it is imperative to consider potential issues within the code.

Cause of the Problem

In this scenario, the password string contained a dollar sign ($), which PHP interpreted as a variable. Consequently, instead of sending the intended password "mypas$word," the application dispatched "mypas," leading to failed database authentication.

Solution

The problem was resolved by escaping the dollar sign with a backslash (). However, a more reliable and efficient solution is to use single quote strings for passwords and other data that should not undergo PHP variable processing.

Escaping the Dollar Sign

Using a backslash to escape the dollar sign allows PHP to treat it as a literal character instead of an instruction to substitute a variable. This approach is adequate but not optimal, as it introduces additional syntax and potential for user error.

Single Quote Strings

Single quote strings are not interpolated and are treated verbatim. This means that PHP will not attempt to process special characters or expand variables within single quote strings, ensuring the preservation of the exact data intended to be stored.

Database Considerations

If the password is retrieved from a database, the same principles apply. The password should be stored within a single quote string within the database in order to prevent any misinterpretation by PHP.

Best Practices

To avoid these types of issues, it is recommended to adhere to the following best practices:

• Use single quote strings for passwords and other sensitive data.
• Escape special characters when using double quote strings.
• Exercise caution when using dollar signs and other characters that may be interpreted as variables.
• Validate input to ensure the expected data format is being provided.

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