php regex escaping special characters

Question

I wrote the following code (yes it does work) and was wondering why I don't need to escape the '<' and '>' characters inside the pattern since they are considered 'special' characters by the php manual.

http://www.php.net/manual/en/function.preg-quote.php

var_dump(preg_match('/<[A-Za-z][A-Za-z0-9]*>/', "<html>", $matches));

echo "<pre>";
var_dump(htmlentities($matches[0]));
echo "</pre>";

output:

int(1) 
string(12) "<html>"

Define “special” character. All characters are special in their own way, you know. :) — tchrist, Mar 10 '13 at 00:29

score 21 · Accepted Answer · edited Jul 24 '15 at 04:21

Only the characters listed on this page need to be escaped in PHP regex matching/replacing.

While < and > can act as delimiter, it doesn't need to be escaped in the given example because you already have /(slash) acting as a delimiter.

Referring to the link in question

The preg_quote() function may be used to escape a string for injection into a pattern and its optional second parameter may be used to specify the delimiter to be escaped.

score 3 · Answer 2 · answered Mar 10 '13 at 00:25

< and > aren't meta characters is most contexts.

However they are used as such for:

named capture groups (?P<name>)
lookbehind assertions (?<=...)

So that's why preg_quote plays it safe and escapes them. It's arguably redundant, since escaping ( and ? would be sufficient. But it doesn't hurt either.

php regex escaping special characters

2 Answers2

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