$re = '~\n\n(.*?)Show Abstract - Show Citation~s';
$str = 'Plenary Papers (1)
Peer-reviewed Papers (113)
PLENARY MANUSCRIPTS (1)
First Author Index
Harrer
Plenary Papers
Some title number one
John W. Doe
2018 Physics SOmething Proceedings
Full Text: Download PDF - PER-Central Record
Show Abstract - Show Citation
PEER REVIEWED MANUSCRIPTS (113)
First Author Index
Doe · Doe2 · Doe3 · Jonathan
Peer-reviewed Papers
Some title number two
Alex White, Paul Klee, and Jacson Pollock
2018 Physics Research Conference Proceedings, doi:10.1234/perc.2018.pr.White
Full Text: Download PDF - PER-Central Record
Show Abstract - Show Citation
Some title number three
Suzanne Heck, Alex Someone, John I. Smith, and Andrew Bourgogne
2018 Physics Education Research Conference Proceedings, doi:10.2345/perc.2018.pr.Heck
Full Text: Download PDF - PER-Central Record
Show Abstract - Show Citation
..';
preg_match_all($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