I am having the following code in a php web page:
if (bInserted) echo "abc";
I would expect PHP to give me a syntax error since I forget to add the dollar sign before the variable name. Howver, the page doesn't produce any errors. Instead, it even echoes the "abc" string. I am not really able to understand this.
Your bInserted is interpreted as a constant and, since is not defined (I presume), it is then treated as the string "bInserted", which evaluates to true hence your "abc" is printed.
Anyway, such implicit conversion from constant to string should raise a notice, see the manual.
If you use an undefined constant, PHP assumes that you mean the name of the constant itself, just as if you called it as a string (CONSTANT vs "CONSTANT"). An error of level E_NOTICE will be issued when this happens.
If you really do not see any message, nor on screen nor in the logs, make sure you have set the correct error reporting level, you could for example try
ini_set('display_errors', 1);
error_reporting(E_ALL);
And, by the way, E_ALL is a defined constant in this case!
notice so write something about enabling errors reporting ;)