Split camelCase word into words with php preg_match (Regular Expression)

You can use preg_split as:

$arr = preg_split('/(?=[A-Z])/',$str);

See it

I'm basically splitting the input string just before the uppercase letter. The regex used (?=[A-Z]) matches the point just before a uppercase letter.

You can also use preg_match_all as:

preg_match_all('/((?:^|[A-Z])[a-z]+)/',$str,$matches);

Explanation:

(        - Start of capturing parenthesis.
 (?:     - Start of non-capturing parenthesis.
  ^      - Start anchor.
  |      - Alternation.
  [A-Z]  - Any one capital letter.
 )       - End of non-capturing parenthesis.
 [a-z]+  - one ore more lowercase letter.
)        - End of capturing parenthesis.

I know that this is an old question with an accepted answer, but IMHO there is a better solution:

<?php // test.php Rev:20140412_0800
$ccWord = 'NewNASAModule';
$re = '/(?#! splitCamelCase Rev:20140412)
    # Split camelCase "words". Two global alternatives. Either g1of2:
      (?<=[a-z])      # Position is after a lowercase,
      (?=[A-Z])       # and before an uppercase letter.
    | (?<=[A-Z])      # Or g2of2; Position is after uppercase,
      (?=[A-Z][a-z])  # and before upper-then-lower case.
    /x';
$a = preg_split($re, $ccWord);
$count = count($a);
for ($i = 0; $i < $count; ++$i) {
    printf("Word %d of %d = \"%s\"\n",
        $i + 1, $count, $a[$i]);
}
?>

Note that this regex, (like codaddict's '/(?=[A-Z])/' solution - which works like a charm for well formed camelCase words), matches only a position within the string and consumes no text at all. This solution has the additional benefit that it also works correctly for not-so-well-formed pseudo-camelcase words such as: StartsWithCap and: hasConsecutiveCAPS.

Input:

oneTwoThreeFour
StartsWithCap
hasConsecutiveCAPS
NewNASAModule

Output:

Word 1 of 4 = "one"
Word 2 of 4 = "Two"
Word 3 of 4 = "Three"
Word 4 of 4 = "Four"

Word 1 of 3 = "Starts"
Word 2 of 3 = "With"
Word 3 of 3 = "Cap"

Word 1 of 3 = "has"
Word 2 of 3 = "Consecutive"
Word 3 of 3 = "CAPS"

Word 1 of 3 = "New"
Word 2 of 3 = "NASA"
Word 3 of 3 = "Module"

Edited: 2014-04-12: Modified regex, script and test data to correctly split: "NewNASAModule" case (in response to rr's comment).

While ridgerunner's answer works great, it seems not to work with all-caps substrings that appear in the middle of sentence. I use following and it seems to deal with these just alright:

function splitCamelCase($input)
{
    return preg_split(
        '/(^[^A-Z]+|[A-Z][^A-Z]+)/',
        $input,
        -1, /* no limit for replacement count */
        PREG_SPLIT_NO_EMPTY /*don't return empty elements*/
            | PREG_SPLIT_DELIM_CAPTURE /*don't strip anything from output array*/
    );
}

Some test cases:

assert(splitCamelCase('lowHigh') == ['low', 'High']);
assert(splitCamelCase('WarriorPrincess') == ['Warrior', 'Princess']);
assert(splitCamelCase('SupportSEELE') == ['Support', 'SEELE']);
assert(splitCamelCase('LaunchFLEIAModule') == ['Launch', 'FLEIA', 'Module']);
assert(splitCamelCase('anotherNASATrip') == ['another', 'NASA', 'Trip']);

Split camelCase word into words with php preg_match (Regular Expression)

Input:

Output:

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