What is "~" in regex?

Question

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Tilde operator in Regular expressions

echo preg_replace_callback('~-([a-z])~', function ($match) {
    return strtoupper($match[1]);
}, 'hello-world');

The code is from http://php.net/manual/en/functions.anonymous.php

I searched for what "~" is in regex and did not find an answer.

What does it do?

It appears to be using `~` as a delimiter instead of `/` which is most commonly used. — datasage, Jan 28 '13 at 17:01
Well, I looked into some refs/tuts regarding regex too and did not find any. Then I searched for "~" while I did't know how the symbol is called exactly. I guess there are a lot of people performing this kind of search.. — Michael, Jan 28 '13 at 17:09
I believe you still get the rep if the question is closed, so no worries. — Evan Davis, Jan 28 '13 at 17:10
The other question doesn't have the symbol `~` in its question text. I don't know if SO's search engine searches symbols as keywords but if so, then this question could still be helpful. — Andrew Cheong, Jan 28 '13 at 17:15
Yup, I mentioned that people might seach for that and while on page the first big H1 contains the symbol, it is a SEO way to get people faster to the answer.. — Michael, Jan 28 '13 at 17:17

Andrew Cheong · Accepted Answer · 2013-01-28T17:02:54.950

The first and last character of a regular expression in PHP (and other implementations) is known as the delimiter. Normally, you see a / being used, but in this case, someone chose ~. Read more here.

Not sure why ~ was chosen though; probably a habit of that particular developer. Normally, one chooses a different delimiter over / when the regular expression itself will contain slashes (e.g. matching URLs), so that slashes don't need to be escaped every time.

score 2 · Answer 2 · edited Jan 28 '13 at 17:11

2

The symbol ~ is just used as delimiter in PHP regexps.

edited Jan 28 '13 at 17:11

Lightness Races in Orbit

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answered Jan 28 '13 at 17:02

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What is "~" in regex?

2 Answers2