regexp split string by commas and spaces, but ignore the inside quotes and parentheses

Question

I need split string by commas and spaces, but ignore the inside quotes, single quotes and parentheses

$str = \"Questions, \\\"Quote\\\",\'single quote\',\'co         


        

Answer 1

Well, this works for the data you supplied:

$rgx = <<<'EOT'
/
  [,\s]++
  (?=(?:(?:[^"]*+"){2})*+[^"]*+$)
  (?=(?:(?:[^']*+'){2})*+[^']*+$)
  (?=(?:[^()]*+\([^()]*+\))*+[^()]*+$)
/x
EOT;

The lookaheads assert that if there are any double-quotes, single-quotes or parentheses ahead of the current match position there's an even number of them, and the parens are in balanced pairs (no nesting allowed). That's a quick-and-dirty way to ensure that the current match isn't occurring inside a pair of quotes or parens.

Of course, it assumes the input is well formed. But on the subject of of well-formedness, what about escaped quotes within quotes? What if you have quotes inside parens, or vice-versa? Would this input be legal?

"not a \" quote", 'not a ) quote', (not ",' quotes)

If so, you've got a much more difficult job ahead of you.

Answer 2

This will work only for non-nested parentheses:

    $regex = <<<HERE
    /  "  ( (?:[^"\\\\]++|\\\\.)*+ ) \"
     | '  ( (?:[^'\\\\]++|\\\\.)*+ ) \'
     | \( ( [^)]*                  ) \)
     | [\s,]+
    /x
    HERE;

    $tags = preg_split($regex, $str, -1,
                         PREG_SPLIT_NO_EMPTY
                       | PREG_SPLIT_DELIM_CAPTURE);

The ++ and *+ will consume as much as they can and give nothing back for backtracking. This technique is described in perlre(1) as the most efficient way to do this kind of matching.