PHP Regex: Difference between \s and \\s

Question

I understand \s is used to match white space character, but sometimes I see "\\s" is used in preg match and working fine. For eg:

if (preg_match("/\\s/", $myString)) {
   // there are spaces
}

if (preg_match("/\s/", $myString)) {
   // there are spaces
}

Is there any difference between above two code blocks?

Answer 1

Trying to make sense of the text from the manual.

http://php.net/manual/en/regexp.reference.escape.php

Single and double quoted PHP strings have special meaning of backslash. Thus if \ has to be matched with a regular expression \\, then "\\\\" or '\\\\' must be used in PHP code.

I might not be correct but here I go.

When you use something like

preg_match("/\\s/", $myString)

What it is doing is converting \\ to \, which in turns make the string to be \s thus it behaves normally i.e its meaning doesn't change and the created regex is '/\s/' internally which matches "spaces"

To match \s in a string you would have to do something as follows

preg_match("/\\\\s/", $myString)

So the answer is \s or \\s in the regex string doesn't make any difference, personally I think using \s is simpler and easy to understand.