Question

To use a simplified example, I have:

$str = "Hello :special_text:! Look, I can write \:special_text:";
$pattern = /*???*/":special_text:";
$res = preg_replace($pattern, 'world', $str);
$res = str_replace("/:", ":", $res);
$res === "Hello world! Look, I can write :special_text:"; // => true

In other words, I’d like to be able to “escape” something that I’m writing.

I think that I have something almost working (using [^:]? as the first part of pattern), but I don’t think that works if $str === ":special_text:", in that^doesn't match[^:]?`.

Answer 1

You can use a negative lookbehind:

(?<!\\):special_text:

This says “replace a :special_text: that isn’t preceded by a backslash”.

In your second str_replace looks like you want to replace \: by :.

See it in action here.

Also, don’t forget if you use backslash in PHP strings you need to escape them once more (if you want a literal \ you need to use PHP \\, and to get a literal \\ you need to use PHP \\\\:

$pattern = '@(?<!\\\\):([^:]+):@';

Here the @ is just a regex delimiter.