如果没有后跟n，如何替换所有出现的\？

Question

Seems to be relatively simple task that gets me stuck in one PHP application. I have a string which has a bunch of in it. Those are fine and need to stay there. However, there are also single occurrences of the character \ and those I need to replace or remove, let's just say with empty character without removing the ones that are followed by n.

The best I came up with was to first replace all with something else, some weird character, then replace the remaining \ with empty space and then convert back the weird character to . However, that seems to be a waste of time and resources, besides, nothing guarantees me that I'll find weird enough character that will never be encountered in the rest of the string...

Any tips?

Answer 1

You need

$s = preg_replace('~\\\\(?!n)~', '', $s);

See the PHP demo:

$s = '\
 \\t \\';
$s = preg_replace('~\\\\(?!n)~', '', $s);
echo $s; // => 
 t 

We need 4 backslashes to pass 2 literal backslashes to the regex engine to match 1 literal backslash in the input string. The (?!n) is a negative lookahead that fails all matches of a backslash that is immediately followed with n.