问题
I want to remove all \r \n \r\n which is pretty easy to so I wrote:
str_replace(array("\r","\n"),"",$text);
but I saw this line:
str_replace(array("\r","\n","\\r","\\n"),"",$text);
and I was wondering what is the double backslash means \\r and \\n.
回答1:
\ is an escape character, it's used to escape the following character.
In "\n", the backslash escapes n and the result will be a new line character.
In "\\n", the first backslash escapes the second backslash and the n is kept as is, so the result is a string containing \n (literally).
See the PHP official documentation > Strings.
In the context of your question, str_replace() will remove new lines ("\n" and "\r") and also remove \n and \r from the string ("\\n" and "\\r" respectively). There's no reason a text contains the words \n and \r, so it seems that using "\\n" and "\\r" has no interest here.
回答2:
The first backslash escapes the second one, so it matches a literal backslash in $text.
I'm not sure why you would want to match that if you just want to remove newlines and carriage returns from the string.
来源：https://stackoverflow.com/questions/27290840/in-phps-str-replace-what-does-the-double-backslash-mean