$re = '/([a-z0-9]|(?=[A-Z]))([A-Z])/m';
$str = 'constants.js
elements.js
event-listener
onClickAddProductButton.js
onClickBackButton.js
onClickCategoryItem.js
onClickDeleteButton.js
onClickFilterByButtons.js
onClickInstallerCheckbox.js
onClickNextButton.js
onClickProductItem.js
onClickQuantityButtons.js
onClickRequestNowButton.js
onClickRestartButton.js
onClickSubmitButton.js
onInputProductSearch.js
onSubmitForm.js
event-listener.js
methods
addProductToCalculationTable.js
addProductToProductSelection.js
addProductToStorage.js
adjustProductQuantity.js
createProduct.js
deleteProduct.js
elementsVisibility.js
filterVisibility.js
formatPriceToTwoDecimals.js
formatProductPrice.js
getRateTableProductHtml.js
getSelectedProductHtml.js
hideAllProducts.js
hideElement.js
initCurrentState.js
initIndicators.js
initSelectedProducts.js
initSteps.js
showAllProducts.js
showElement.js
successVisibility.js
updateCalculationTableProductPrices.js
updateCalculationTableTotals.js
updateProductQuantityNumbers.js
updateSummary.js
methods.js
storage.js
';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php