Echoing session variables in php

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I know that in
php I can put a variable name inside a quoted string when I use echo, but I apparently
can't do this with a session variable. Can anyone explain why?

Here is the code, with the "offending" php
commented
out:

session_start();

$test
            = 100;
$_SESSION['test'] =
            200;
?>

 

            
 

            
 
            />");?>
 
            />");?>

 
            echo($_SESSION['test']."
");?>
 
            //echo("$_SESSION['test']"."
");?>

            

And
the output looks like
this:

100


100

200

But
if I uncomment the offending code
line:

 
            echo("$_SESSION['test']"."            />");?>

I
get no output and the following
error:

Parse error: syntax error,
            unexpected T_ENCAPSED_AND_WHITESPACE, expecting T_STRING or T_VARIABLE or T_NUM_STRING
            in - on line 14

So I
can go on my merry way knowing how to do it correctly (just keep the session variable
outside of the double quotes), but I would really like to understand why this doesn't
work for session
variables.

Thanks!

Answer

Inside a double-quoted string you must
enclose a complex variable (array or object property) in
{}:

            echo("{$_SESSION['test']}"."            />");?>

This
isn't an issue with $_SESSION specifically, but any array
accessed by quoted keys. Note, that you can include a numerically
indexed array value with wrapping in {}, as in
"echo $array[2] is two";