preg_replace - NULL result?

Question

Here's a small example (download, rename to .php and execute it in your shell):

test.txt

Why does preg_replace return NULL instead of the original string?

\x{2192} is the same as HTML "→" ("→").

Answer 1

From the documentation on preg_replace():

Return Values

preg_replace() returns an array if the subject parameter is an array, or a string otherwise.

If matches are found, the new subject will be returned, otherwise subject will be returned unchanged or NULL if an error occurred.

In your pattern, I don't think the u flag is supported. WRONG

Edit: It seems like some kind of encoding issue with the subject. When I erase '147 3.2 V6 - GTA (184 kW)' and manually re-type it everything seems to work.

Edit 2: In the pattern you provided, there are 3 spaces that seem to be giving issues to the regex engine. When I convert them to decimal their value is 160 (as opposed to normal space 32). When I replace those spaces with normal ones it seems to work.

I've replaced the offending spaces with underscores below:

'147 3.2 V6 - GTA (184 kW)'
'147 3.2_V6 - GTA_(184_kW)'

Answer 2

I believe there is also a fault in your Regex expression: ~\x{2192}~u

Try replacing what I have and see if that works out for you: /\x{2192}/u

Answer 3

• You are using single quotes, which means the only thing that you can escape is other single quotes. To enable escape sequences (e.g. \x32, then use double quotes "")
• I am not a UTF8 expert, but the escape code \x2192 is not correct either. You can do: \x21\x92 to get both bytes into your string, but you may want to look at utf8_encode and utf8_decode
• Your source string has invalid characters in it, or something. PHP gives: Warning: preg_replace(): Compilation failed: invalid UTF-8 string at offset 0 in test.php on line 7