Re: Re: Parsing variables within string variables

At 02:41 PM 4/7/2006, David Clough wrote:

I have to parse the string 'Hello $foo' as it comes from the database: I don't get to construct it. I did hold out more hope for the eval function, but it seems to me that this is for PHP code in a database, not to evaluate variables.

David, please try the eval() route: it will do what you want. You say, "this is for PHP code in a database, not to evaluate variables," but evaluating variables is absolutely part of PHP code processing! Eval() will operate on "$x = 4;" just as easily as on "Hello $foo." You should not use eval() frivolously because it presents a potential vulnerability in your code. You may wish to ensure that the database text it operates on is first cleansed of any other PHP syntax -- similarly to the way we should all ensure that any incoming data is clean before we process it and incorporate it into our scripts. Here's an example of variaible evaluation: _______________________ $bar = "cat"; $foo = "Hello \$bar."; echo $foo; RESULT: Hello $bar. By escaping the $, I have made it a literal character in the text, the same as if I'd read "Hello $bar" from a database. _______________________ eval("echo \"$foo\";"); RESULT: Hello cat. This is equivalent to scripting:

        echo "$foo";
I'm using eval() to execute the echo command and interpret the PHP variable $foo.

_______________________ eval("\$dog = \$bar;"); echo "dog = " . $dog; RESULT: dog = cat Here I'm using eval() to set one PHP variable equal to another. _______________________ You can't simply write:

        eval("\$bar;");

or

        $x = eval($foo);

because everything inside the eval() parentheses needs to be a complete PHP statement. The eval() function itself doesn't return the value of an evaluated expression. To capture the value of an expression, you must evaluate a complete statement that sets a variable equal to the expression as above. _______________________ Clear as mud? Regards, Paul