PHP concatenation override

Question

Is it possible to change a concatened string, with a variable in the string?

  $x = 'XXX' . $y;

Is there a way to have $x contain 'XXY', without changing this?

What do I need to set in $y for this? Does there exist something like a "remove previous character"?

EDIT:

Maybe i didnt made myself crystal clear:

$y needs to be a string, no functions or anything. Its due to discover an exploit...

Related: [javascript version of what this question is getting at](http://stackoverflow.com/questions/11891653/javascript-concat-string-with-backspace) — James Thorpe, Feb 27 '15 at 13:55
Little context or a bit more information would be good. In the given code sample is not exactly clear what are you trying to achieve — DaGhostman Dimitrov, Feb 27 '15 at 13:58
@JayBlanchard *Bah-dah-bump Kah-Rraaaash!!!* < cymbal crash sound - *salut Sam* — Funk Forty Niner, Feb 27 '15 at 14:26
If you cannot use functions then there is no way to do what you're asking in the browser. — Jay Blanchard, Mar 02 '15 at 12:44

Matías Cánepa · Answer 1 · 2015-02-27T14:07:56.573

1

$x = substr("XXX", 0, -1) . $y;

In light of your edit, I don't think you can do what you want the way you want it to happen.

edited Feb 27 '15 at 14:07

answered Feb 27 '15 at 13:56

Matías Cánepa

you are changing the value of $x, not $y. I think the author just wants to see if there are some gotchas in PHP string concatenation implementation. – Laurynas Tretjakovas Feb 27 '15 at 13:59
I think the OP wants to change `$x` @LaurynasTretjakovas "so that `$x` would contain XXY" – Jay Blanchard Feb 27 '15 at 14:00

score 1 · Answer 2 · answered Feb 27 '15 at 13:56

1

Not that I know of, but you can use substr_replace:

$x = substr_replace($x, $y, -1);

If you want to replace the exact number of characters in $y at the end of $x:

$x = substr_replace($x, $y, -(strlen($y));

answered Feb 27 '15 at 13:56

sjagr

score 0 · Answer 3 · answered Feb 27 '15 at 13:58

0

Just set the value of $y to a backspace character plus 'Y':

$y = chr(8) . 'Y';

answered Feb 27 '15 at 13:58

littleibex

3

This doesn't work, the result is 'XXXY' when the OP wants 'XXY' [EXAMPLE](http://phpfiddle.org/lite/code/vgat-6z0w) – Jay Blanchard Feb 27 '15 at 14:05
1

This *does* work in the CLI we just don't know what the OP's intent is. – Jay Blanchard Feb 27 '15 at 14:18

score -1 · Answer 4 · answered Feb 27 '15 at 14:04

-1

Try this:

$y = chr(8).'Y';
$x = 'XXX' . $y;

chr(8) should give you a backspace character.

answered Feb 27 '15 at 14:04

Headshota

`var_dump($x)` is `string(5) "XXXY"` – sjagr Feb 27 '15 at 14:06
It doesn't work - [EXAMPLE](http://phpfiddle.org/lite/code/vgat-6z0w) – Jay Blanchard Feb 27 '15 at 14:07
PHPFiddle is probably sanitizing the characters, try running it locally. it works for me. – Headshota Feb 27 '15 at 14:08
I ran it locally and it didn't work. – Jay Blanchard Feb 27 '15 at 14:09
What's the php version? – Headshota Feb 27 '15 at 14:09
5.3.3 on one server, 5.6.2 on another. PHP fiddle doesn't sanitize stuff like this. What version are you running? – Jay Blanchard Feb 27 '15 at 14:12
Are you outputing the data in browser? or CLI? – Headshota Feb 27 '15 at 14:12
Browser. Let me try CLI. – Jay Blanchard Feb 27 '15 at 14:14
I assume the backspace escape sequence won't be recognized by the browser, only by CLI. – Headshota Feb 27 '15 at 14:16
It works in the CLI. Unfortunately we do not know how the OP wants to use. – Jay Blanchard Feb 27 '15 at 14:17
It has to work in non-cli but you exactly understood what i want to achieve! I cant use functions $y got to be a string. – Michael Leiss Mar 02 '15 at 08:27

4 Answers4