$re = '/(?:(?<![\w-])(?=[\w-])|(?<=[\w-])(?![\w-]))(0o|0s|3a|3b|3d|6b|6o|a|a1|a2|a3|a4|ab|able|about|above|abst|ac|accordance|according|accordingly|across|act|actually|ad|added|adj|ae|af|affected|affecting|affects|after|afterwards|ag|again|against|ah|ain|ain\'t|aj|al|all|allow|allows|almost|alone|along|already|also|although|always|am|among|amongst|amoungst|amount|an|and|announce|another|any|anybody|anyhow|anymore|anyone|anything|anyway|anyways|anywhere|ao|ap|apart|apparently|appear|appreciate|appropriate|approximately|ar|are|aren|arent|aren\'t|arise|around|as|a\'s|aside|ask|asking|associated|at|au|auth|av|available|aw|away|awfully|ax|ay|az|b|b1|b2|b3|ba|back|bc|bd|be|became|because|become|becomes|becoming|been|before|beforehand|begin|beginning|beginnings|begins|behind|being|believe|below|beside|besides|best|better|between|beyond|bi|bill|biol|bj|bk|bl|bn|both|bottom|bp|br|brief|briefly|bs|bt|bu|but|bx|by|c|c1|c2|c3|ca|call|came|can|cannot|cant|can\'t|cause|causes|cc|cd|ce|certain|certainly|cf|cg|ch|changes|ci|cit|cj|cl|clearly|cm|c\'mon|cn|co|com|come|comes|con|concerning|consequently|consider|considering|contain|containing|contains|corresponding|could|couldn|couldnt|couldn\'t|course|cp|cq|cr|cry|cs|c\'s|ct|cu|currently|cv|cx|cy|cz|d|d2|da|date|dc|dd|de|definitely|describe|described|despite|detail|df|di|did|didn|didn\'t|different|dj|dk|dl|do|does|doesn|doesn\'t|doing|don|done|don\'t|down|downwards|dp|dr|ds|dt|du|due|during|dx|dy|e|e2|e3|ea|each|ec|ed|edu|ee|ef|effect|eg|ei|eight|eighty|either|ej|el|eleven|else|elsewhere|em|empty|en|end|ending|enough|entirely|eo|ep|eq|er|es|especially|est|et|et-al|etc|eu|ev|even|ever|every|everybody|everyone|everything|everywhere|ex|exactly|example|except|ey|f|f2|fa|far|fc|few|ff|fi|fifteen|fifth|fify|fill|find|fire|first|five|fix|fj|fl|fn|fo|followed|following|follows|for|former|formerly|forth|forty|found|four|fr|from|front|fs|ft|fu|full|further|furthermore|fy|g|ga|gave|ge|get|gets|getting|gi|give|given|gives|giving|gj|gl|go|goes|going|gone|got|gotten|gr|greetings|gs|gy|h|h2|h3|had|hadn|hadn\'t|happens|hardly|has|hasn|hasnt|hasn\'t|have|haven|haven\'t|having|he|hed|he\'d|he\'ll|hello|help|hence|her|here|hereafter|hereby|herein|heres|here\'s|hereupon|hers|herself|hes|he\'s|hh|hi|hid|him|himself|his|hither|hj|ho|home|hopefully|how|howbeit|however|how\'s|hr|hs|http|hu|hundred|hy|i|i2|i3|i4|i6|i7|i8|ia|ib|ibid|ic|id|i\'d|ie|if|ig|ignored|ih|ii|ij|il|i\'ll|im|i\'m|immediate|immediately|importance|important|in|inasmuch|inc|indeed|index|indicate|indicated|indicates|information|inner|insofar|instead|interest|into|invention|inward|io|ip|iq|ir|is|isn|isn\'t|it|itd|it\'d|it\'ll|its|it\'s|itself|iv|i\'ve|ix|iy|iz|j|jj|jr|js|jt|ju|just|k|ke|keep|keeps|kept|kg|kj|km|know|known|knows|ko|l|l2|la|largely|last|lately|later|latter|latterly|lb|lc|le|least|les|less|lest|let|lets|let\'s|lf|like|liked|likely|line|little|lj|ll|ll|ln|lo|look|looking|looks|los|lr|ls|lt|ltd|m|m2|ma|made|mainly|make|makes|many|may|maybe|me|mean|means|meantime|meanwhile|merely|mg|might|mightn|mightn\'t|mill|million|mine|miss|ml|mn|mo|more|moreover|most|mostly|move|mr|mrs|ms|mt|mu|much|mug|must|mustn|mustn\'t|my|myself|n|n2|na|name|namely|nay|nc|nd|ne|near|nearly|necessarily|necessary|need|needn|needn\'t|needs|neither|never|nevertheless|new|next|ng|ni|nine|ninety|nj|nl|nn|no|nobody|non|none|nonetheless|noone|nor|normally|nos|not|noted|nothing|novel|now|nowhere|nr|ns|nt|ny|o|oa|ob|obtain|obtained|obviously|oc|od|of|off|often|og|oh|oi|oj|ok|okay|ol|old|om|omitted|on|once|one|ones|only|onto|oo|op|oq|or|ord|os|ot|other|others|otherwise|ou|ought|our|ours|ourselves|out|outside|over|overall|ow|owing|own|ox|oz|p|p1|p2|p3|page|pagecount|pages|par|part|particular|particularly|pas|past|pc|pd|pe|per|perhaps|pf|ph|pi|pj|pk|pl|placed|please|plus|pm|pn|po|poorly|possible|possibly|potentially|pp|pq|pr|predominantly|present|presumably|previously|primarily|probably|promptly|proud|provides|ps|pt|pu|put|py|q|qj|qu|que|quickly|quite|qv|r|r2|ra|ran|rather|rc|rd|re|readily|really|reasonably|recent|recently|ref|refs|regarding|regardless|regards|related|relatively|research|research-articl|respectively|resulted|resulting|results|rf|rh|ri|right|rj|rl|rm|rn|ro|rq|rr|rs|rt|ru|run|rv|ry|s|s2|sa|said|same|saw|say|saying|says|sc|sd|se|sec|second|secondly|section|see|seeing|seem|seemed|seeming|seems|seen|self|selves|sensible|sent|serious|seriously|seven|several|sf|shall|shan|shan\'t|she|shed|she\'d|she\'ll|shes|she\'s|should|shouldn|shouldn\'t|should\'ve|show|showed|shown|showns|shows|si|side|significant|significantly|similar|similarly|since|sincere|six|sixty|sj|sl|slightly|sm|sn|so|some|somebody|somehow|someone|somethan|something|sometime|sometimes|somewhat|somewhere|soon|sorry|sp|specifically|specified|specify|specifying|sq|sr|ss|st|still|stop|strongly|sub|substantially|successfully|such|sufficiently|suggest|sup|sure|sy|system|sz|t|t1|t2|t3|take|taken|taking|tb|tc|td|te|tell|ten|tends|tf|th|than|thank|thanks|thanx|that|that\'ll|thats|that\'s|that\'ve|the|their|theirs|them|themselves|then|thence|there|thereafter|thereby|thered|therefore|therein|there\'ll|thereof|therere|theres|there\'s|thereto|thereupon|there\'ve|these|they|theyd|they\'d|they\'ll|theyre|they\'re|they\'ve|thickv|thin|think|third|this|thorough|thoroughly|those|thou|though|thoughh|thousand|three|throug|through|throughout|thru|thus|ti|til|tip|tj|tl|tm|tn|to|together|too|took|top|toward|towards|tp|tq|tr|tried|tries|truly|try|trying|ts|t\'s|tt|tv|twelve|twenty|twice|two|tx|u|u201d|ue|ui|uj|uk|um|un|under|unfortunately|unless|unlike|unlikely|until|unto|uo|up|upon|ups|ur|us|use|used|useful|usefully|usefulness|uses|using|usually|ut|v|va|value|various|vd|ve|ve|very|via|viz|vj|vo|vol|vols|volumtype|vq|vs|vt|vu|w|wa|want|wants|was|wasn|wasnt|wasn\'t|way|we|wed|we\'d|welcome|well|we\'ll|well-b|went|were|we\'re|weren|werent|weren\'t|we\'ve|what|whatever|what\'ll|whats|what\'s|when|whence|whenever|when\'s|where|whereafter|whereas|whereby|wherein|wheres|where\'s|whereupon|wherever|whether|which|while|whim|whither|who|whod|whoever|whole|who\'ll|whom|whomever|whos|who\'s|whose|why|why\'s|wi|widely|will|willing|wish|with|within|without|wo|won|wonder|wont|won\'t|words|world|would|wouldn|wouldnt|wouldn\'t|www|x|x1|x2|x3|xf|xi|xj|xk|xl|xn|xo|xs|xt|xv|xx|y|y2|yes|yet|yj|yl|you|youd|you\'d|you\'ll|your|youre|you\'re|yours|yourself|yourselves|you\'ve|yr|ys|yt|z|zero|zi|zz)(?:(?<![\w-])(?=[\w-])|(?<=[\w-])(?![\w-]))\s?/m';
$str = 'hello-a
a
';
preg_match_all($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