Split string by delimiter, but not if it is escaped

Question

How can I split a string by a delimiter, but not if it is escaped? For example, I have a string:

1|2\\|2|3\\\\|4\\\\\\|4

The delimiter is <

Answer 1

For future readers, here is a universal solution. It is based on NikiC's idea with (*SKIP)(*FAIL):

function split_escaped($delimiter, $escaper, $text)
{
    $d = preg_quote($delimiter, "~");
    $e = preg_quote($escaper, "~");
    $tokens = preg_split(
        '~' . $e . '(' . $e . '|' . $d . ')(*SKIP)(*FAIL)|' . $d . '~',
        $text
    );
    $escaperReplacement = str_replace(['\\', '$'], ['\\\\', '\\$'], $escaper);
    $delimiterReplacement = str_replace(['\\', '$'], ['\\\\', '\\$'], $delimiter);
    return preg_replace(
        ['~' . $e . $e . '~', '~' . $e . $d . '~'],
        [$escaperReplacement, $delimiterReplacement],
        $tokens
    );
}

Make a try:

// the base situation:
$text = "asdf\\,fds\\,ddf,\\\\,f\\,,dd";
$delimiter = ",";
$escaper = "\\";
print_r(split_escaped($delimiter, $escaper, $text));

// other signs:
$text = "dk!%fj%slak!%df!!jlskj%%dfl%isr%!%%jlf";
$delimiter = "%";
$escaper = "!";
print_r(split_escaped($delimiter, $escaper, $text));

// delimiter with multiple characters:
$text = "aksd()jflaksd())jflkas(('()j()fkl'()()as()d('')jf";
$delimiter = "()";
$escaper = "'";
print_r(split_escaped($delimiter, $escaper, $text));

// escaper is same as delimiter:
$text = "asfl''asjf'lkas'''jfkl''d'jsl";
$delimiter = "'";
$escaper = "'";
print_r(split_escaped($delimiter, $escaper, $text));

Output:

Array
(
    [0] => asdf,fds,ddf
    [1] => \
    [2] => f,
    [3] => dd
)
Array
(
    [0] => dk%fj
    [1] => slak%df!jlskj
    [2] => 
    [3] => dfl
    [4] => isr
    [5] => %
    [6] => jlf
    )
Array
(
    [0] => aksd
    [1] => jflaksd
    [2] => )jfl'kas((()j
    [3] => fkl()
    [4] => as
    [5] => d(')jf
)
Array
(
    [0] => asfl'asjf
    [1] => lkas'
    [2] => jfkl'd
    [3] => jsl
)

Note: There is a theoretical level problem: implode('::', ['a:', ':b']) and implode('::', ['a', '', 'b']) result the same string: 'a::::b'. Imploding can be also an interesting problem.