eval
Evaluate a string as PHP code
Description
mixed eval(string $code)
The code being evaluated inherits the
variable scope
of the line on which the eval call occurs.
Any variables available at that line will be available for reading and
modification in the evaluated code.
However, all functions and classes defined will be defined in the global namespace.
In other words, the compiler considers the evaluated code as if it were a
separate included file.
Caution
The eval language construct is very dangerous
because it allows execution of arbitrary PHP code. Its use thus is
discouraged. If you have carefully verified that there is no other option
than to use this construct, pay special attention not to pass any user
provided data into it without properly validating it beforehand.
Parameters
-
code
-
Valid PHP code to be evaluated.
The code must not be wrapped in opening and closing
PHP tags, i.e.
'echo "Hi!";' must be passed instead of
'<?php echo "Hi!"; ?>'. It is still possible to leave and
re-enter PHP mode though using the appropriate PHP tags, e.g.
'echo "In PHP mode!"; ?>In HTML mode!<?php echo "Back in PHP mode!";'.
Apart from that the passed code must be valid PHP. This includes that all statements
must be properly terminated using a semicolon.
'echo "Hi!"' for example will cause a parse error, whereas
'echo "Hi!";' will work.
A return statement will immediately terminate the
evaluation of the code.
The code will be executed in the scope of the code calling eval. Thus any
variables defined or changed in the eval call will remain visible after
it terminates.
Return Values
eval returns null unless
return is called in the evaluated code, in which case
the value passed to return is returned. As of PHP 7, if there is a
parse error in the evaluated code, eval throws a ParseError exception.
Before PHP 7, in this case eval returned
false and execution of the following code continued normally. It is
not possible to catch a parse error in eval
using set_error_handler.
Examples
Example #1 eval example - simple text merge
<?php
$string = 'cup';
$name = 'coffee';
$str = 'This is a $string with my $name in it.';
echo $str. "\n";
eval("\$str = \"$str\";");
echo $str. "\n";
?>
The above example will output:
This is a $string with my $name in it.
This is a cup with my coffee in it.
Notes
Note: Because this is a
language construct and not a function, it cannot be called using
variable functions,
or named arguments.
TipAs with anything that outputs
its result directly to the browser, the output-control functions can be used to capture
the output of this function, and save it in a
string (for example).
Note:
In case of a fatal error in the evaluated code, the whole script exits.