preg_replace（）转义：单反双反斜杠？

Question

I noticed someone using preg_replace() with double backslashes to escape, (e.g., <\\/div> instead of <\/div>).

Is this necessary? I tried both ways and I don't see what's the difference.

simple example...

preg_replace('/<div>\\s*text<\\/div>/', '', $somestring);

vs

preg_replace('/<div>\s*text<\/div>/', '', $somestring);

Answer 1

A backslash in a PHP string literal can have a special meaning. For example " " is a newline, not the string " ". To write the string " ", you need to escape the backslash as "\ ". However, if the character following the backslash doesn't have any special meaning, the backslash is taken as is. E.g. "\foo" is the string "\foo". In single-quoted strings there's only a single case in which you need to escape the backslash, which is directly before the end of the string: 'foo\\' → "foo\".

So, writing \\/ in a PHP string literal or \/ has the same meaning, because / does not have any special significance to PHP. Either way is correct. This is not about regex syntax but about PHP syntax.