Regex to replace spaces and brackets with underscore

Question

I have some strings in the following formats:

this is a string
This is a string
This is a (string)
This is a  string

and i want a regex convert it to the following:

this_is_a_string

with no leading

I have the following using preg_replace which is getting me almost all of the way:

preg_replace('/[^A-Za-z]+/', '_', $string)

However, it converts the last ) to an underscore which is not acceptable for my uses. I could easily trim that off in a separate function but im wondering if its possible to do with a single regex?

It looks like you might be wanting to make a URL slug. If so, I bet that if you search for "regex to build a URL slug" you could find your answer. — Andy Lester
– Andy Lester, Commented Aug 23, 2013 at 19:52

Casimir et Hippolyte · Accepted Answer · 2013-08-23 19:11:27Z

2

$result = preg_replace('~[^A-Z]+([A-Z]+)(?:[^A-Z]+$)?~i', '_$1', $string);

edited Aug 23, 2013 at 19:11

answered Aug 23, 2013 at 19:05

Casimir et Hippolyte

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1 Comment

anubhava Over a year ago

+1 just make it: strtolower(preg_replace('~[^A-Z]+([A-Z]+)(?:[^A-Z]+$)?~i', '_$1', $string));

Enissay · Accepted Answer · 2013-08-23 21:52:14Z

1

$result = preg_replace('~([^a-zA-Z\n\r()]+)~', '_', $string);

Try it HERE

Be sure tehre's no trailing or leading spaces in your string or it will be replaced too... Use trim($string) to remove it

edited Aug 23, 2013 at 21:52

answered Aug 23, 2013 at 19:25

Enissay

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3 Comments

Funk Forty Niner Over a year ago

Actually, I deleted my answer. I was told that I wasn't covering most of the OP's issues. preg_replace is the best method to use. Thanks for the mention though, cheers.

Enissay Over a year ago

@Fred-ii-, Ow, I didnt really checked your code, but the idea wasnt bad xD

Funk Forty Niner Over a year ago

True, however it did not address the parentheses aspect.

p.s.w.g · Accepted Answer · 2013-08-23 19:21:30Z

0

Regular expressions are a great tool, but there are some things they're not well suited for. Converting the case of characters is one thing regular expressions alone can't do. You could use the preg_replace_callback function to transform the matched text to lowercase, but this is actually pretty straight forward to accomplish by simply changing your logic around a bit.

Perhaps something like this instead:

$string = 'This is a (string)';
preg_match_all("/[a-zA-Z]+/", $string, $matches);
$string = strtolower(implode('_', $matches[0])); // this_is_a_string

edited Aug 23, 2013 at 19:21

answered Aug 23, 2013 at 19:08

p.s.w.g

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4 Comments

Funk Forty Niner Over a year ago

Thanks for pointing that out to me earlier, I deleted my answer. Yours is obviously the correct method.

revo Over a year ago

more practical if replace pattern with \w+

p.s.w.g Over a year ago

@revo yes I considered that (in fact that's how I wrote it originally), but I suspect OP is trying to make a slug for a URL that's written in Latin letters only.

revo Over a year ago

But I saw formats are limited to 4 numbers & I'm in love with best shortest ways.

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