Which PHP function is used to evaluate the contents of a string as PHP code?

The function used to evaluate the contents of a string as PHP code is eval(). This function takes a string as its argument and treats the string as PHP code, executing it within the current scope. When invoked, eval() compiles the string and executes it, effectively allowing the dynamic execution of code.

This capability can be particularly useful in scenarios where there is a need to evaluate code stored in a string, such as from user inputs or dynamic generation of code. However, it should be used with caution due to security risks, such as code injection vulnerabilities, if the input is not properly sanitized.

The other choices listed do not fulfill this function within PHP. For instance, functions like execute(), run(), and execute_string() do not exist in PHP for the purpose of evaluating string content as code. Thus, eval() stands out as the correct and specific function designed for this operation.