PHP Replace empty line mismatch empty line problem solution

A blank line, which may include, line breaks, &nbsp, and spaces. When processing a string, it is unavoidable to encounter a blank line processing.
1, replace blank lines, blank lines can include spaces,  ,\t,\f,\n

$s = preg_replace ('/(^ (\s| ) *$)/M ', ', $s);
2, replace blank lines, including line breaks only

$s = preg_replace ('/($\n\r*$) | ( ^\n\r*^)) +/m ', ', $s)
3, replace the blank line, and remove the whitespace from the beginning and end of the Non-empty line

$s = preg_replace ('/^ ( |\s) *| (  |\s) *$/m ', ', $s);
4, does not match the blank line, directly does not match the blank line, is very difficult. Actually does not match the blank line, is matches the Non-empty line

Preg_match_all ('/\s+/m ', $s, $match);
5, multiple-line matching instance

$s =  
 
 test:
 11111
 22222
 
 33333333333333333333 br>  44444444444444444444
  "; 
 
$s = preg_replace ('/(^ (\s|&nbsp;) *$)/M ', ' <br > ', $s); 
 
$pa = "/test: ((\s) *[^<]*) *)/I"; 
Preg_match ($pa, $s, $m); 
 
Echo $m [1]; 
matches the null and void between rows from the test line to the bottom, and is also 11111,22222
6, characters in the common matching pattern
I mode will match both the uppercase and lowercase letters
m strings as multiple lines
S treats the string as a single line, and the newline character as a normal character
X ignores the white space in the pattern by ignoring the
e preg_replace () function to replace the reverse reference in the replacement string, using it as a PHP code evaluation and replacing the searched string with its result.
A forces only the beginning of the target string to match
the $ metacharacters in D mode match only the end of the target string
U matches the nearest string
U pattern string is treated as UTF-8