Perform calculation inside php string

Question

I have a string like

$str = "23 + %%val%%";

Now, if I wanted to perform this calculation giving %%val%% a value, e.g. 20, how could I do?

`$str = "" . (23 + $val);` – Jeff Lambert Sep 16 '14 at 15:20 — Jeff Lambert, Sep 16 '14 at 15:20
23 is in the $str togheter with $val :( – user3707352 Sep 17 '14 at 16:25 — user3707352, Sep 17 '14 at 16:25

score 1 · Answer 1 · answered Sep 16 '14 at 15:20

1

You can't. PHP isn't recursively executable, unless you use eval() (DON'T use eval()). Why can't you just do

$str = 23 + $val;

?

answered Sep 16 '14 at 15:20

Marc B

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Because 23 is inside $str :( – user3707352 Sep 17 '14 at 16:23

score 0 · Answer 2 · edited May 23 '17 at 12:12

0

$a = 10;
$b = 10;
$c = 10;
$string = "a + b + c";

$result = eval('return ' . preg_replace('/([a-zA-Z0-9])+/', '\$$1', $string) . ';');
echo $result;

this will echo 30.

there is another post about this here Calculate a sum in a string

edited May 23 '17 at 12:12

Community

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answered Sep 16 '14 at 15:22

Maantje

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score 0 · Answer 3 · answered Sep 16 '14 at 15:34

0

$str = "23 + {$value}"

Then to perform the calculation, you'd need a function that takes a string and breaks up the integers and operators. Seems like a waste since php is not strongly typed, and you can easily convert strings to integers.

answered Sep 16 '14 at 15:34

J-Dizzle

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score 0 · Accepted Answer · answered Sep 16 '14 at 15:56

If you really want to keep this format, you can do this :

function calculate($string, $value) {
  return str_replace('%%val%%', $value, $string);
}

$str = "23 + %%val%%";
$value = 25;
$result = eval('return '.calculate($str, $value).';');

var_dump($result); // int(48)

$result = eval('return '.calculate("16 + %%val%%", 10).';');

var_dump($result); // int(26)

But be careful with eval (See : eval())

The eval() language construct is very dangerous because it allows execution of arbitrary PHP code.

Perform calculation inside php string

4 Answers4