How to transform a string to lowercase with preg_replace

Question

I just stuck at this and cannot find solution. I would like to try to transform a string to lower case using preg_replace. I just cannot create the right regex. The reason is that normal strtolower does not support unicode characters. I know that I could use mb_strtolower but this function seems to be quite slow and beside them not everyone has MB support.

Any clue?

Regards, Radek

EDIT: Ok, thanks alot for your help guys. I think my approach was not quite correct. I think it would be much better to use this: How do I detect non-ASCII characters in a string? and then respectively use either the strtolower or mb_strtolower if available.

I'm curios, what makes you think that regex would actually be faster than mb_strtolower? — Andreas Wong, Mar 30 '12 at 08:00
you can use strtolower() php function to convert sting into lower case. — Rukmi Patel, Mar 30 '12 at 08:01
@andreas I did some test. `preg_replace` seems 40-50 times faster than `mb_strtolower`. But ofc i didnt put all the rules — safarov, Mar 30 '12 at 08:18
I'd think that `strtolower` works if you set the correct locale... or am I wrong? Have you tried it with the correct locale? — Tomas, Mar 30 '12 at 08:31

score 5 · Accepted Answer · answered Mar 30 '12 at 08:09

5

Regex is not able to change characters by itself, it can only change their order and/or add additional characters/delete some of them.

There is preg_replace_callback or /e flag, but they can manipulate only with known functions, and therefore can't do better than strtolower.

If you can't rely on existense of mb_strolower function, you will have to implement it yourself.

answered Mar 30 '12 at 08:09

Nameless

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SO it's basically not possible? – Radek Suski Mar 30 '12 at 08:18
Yes, it is basically not possible. Regex is a tool for pattern matching and string recomposition, it can't transform chars on its own. – Nameless Mar 30 '12 at 08:38

score 0 · Answer 2 · answered Mar 30 '12 at 08:14

0

You shouldn't use a preg_replace for this because preg_replace is used to match a certain pattern and replace it with something else. Wat you want is to replace every single uppercase character with a lowercase one, so no need to match a pattern.

mb_strtolower would be the way to go, and if you don't have the mb_ functions you'll have to write a function yourself using a lot of str_replace's...

answered Mar 30 '12 at 08:14

gitaarik

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Yes but mb_stratolower is so damn slow. I did some test with to compare mb_strlower and native strtolower and MB seems to be about 30 times slower than the native one. My biggest problem is that at the time I have to do the strtolower I don't know if I have unicode characters within the string or not. – Radek Suski Mar 30 '12 at 08:21
Maybe first use strtolower, then use preg_replace_callback to replace all characters that are not default lowercase characters (/[^a-z]+/) and then use mb_strtolower for that – gitaarik Mar 30 '12 at 09:07
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I came here because I was looking for a way to "decaptialize" a string (e.g. turn "`The War of NextGen`" to "`the war of nextGen`" - so for this case lower-casing the entire string will NOT work for me. I was trying to use preg_replace with `"/\b(\w)/"` and the replace string as `strtolower("$1")` - but it doesn't work! Surely there should be a way? – Yuval A. Jun 10 '17 at 12:24

How to transform a string to lowercase with preg_replace

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