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I'm trying to strip hidden control chars (especially \x{89} and \x{88}) with preg_replace() from a string. It is "ˆText" (it starts with an "\x{88}" char), mb_detect_encoding says it is UTF-8.

The code used is $result = preg_replace('/\x{88}/u','',$string); but the result is null.

If I use the code without /u modifier I get "�Text", the control char is replaced with a replacement char (U+FFFD).

I'm using PHP 7.1 on Windows. The same search with BBEdit and NotePad++ replaces the chars correctly.

Any ideas?

Thanks, A.

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  • try reading this Commented Dec 25, 2020 at 9:23
  • Thanks, I tried all the solutions but don't work for me. Commented Dec 25, 2020 at 9:29
  • If preg_replace returns null then it is due to an error. Try calling preg_last_error after your preg_replace. Then compare the error code with the errors mentioned in the doc [here] (php.net/manual/en/function.preg-last-error.php) Commented Dec 25, 2020 at 9:34
  • ˆ is not \x{88}, it is \x{2C6}. Also, why not just use str_replace("\u{02C6}", "", $string)? Commented Dec 25, 2020 at 11:24
  • preg_last_error returs code "4" that is PREG_BAD_UTF8_ERROR. Thanks. Commented Dec 25, 2020 at 12:13

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preg_replace() returns "null" only on error. Run preg_last_error() right after preg_replace() and check the returned error code.

As a side note: Your wording suggests that you want to strip all control characters, not just the two explicitly mentioned. Then you would be better of matching against "\p{Cc}"

preg_replace('/\p{Cc}/u', '', $string);
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4 Comments

You are right, the function returns 4/PREG_BAD_UTF8_ERROR error code. The files comes out from a shell_exec pre-processor that should strip all control chars but sometimes fails with some characters. I suppose these files have problem with characters encoding. So I'm trying to fix without success. Thanks.
It fails also with preg_replace('/\p{Cc}/u', '', $string);, same error "4". It seams it is not possibile to parse this string.
The string you are trying to parse is just not valid UTF-8. If you get the String from shell_exec(), the called executable is not delivering the output in UTF-8 charset.
If the script is running on a Linux machine, check the output of the "locale" command. if the default locale is not "xx_XX.UTF-8" but something like xx_XX.ISO8859-1 then that might be the charset your executable is using. you still can convert that with mb_convert_encoding() before running preg_replace()

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