$re = '/\A(?:^(?!.*\bLecture\b).*\r?\n)*|^\r?\n|^.*\r?\n(?![\s\S]*\bLecture\b)/m';
$str = 'My Dashboard
Fnfjfjf. random test
00:50
1:01:56
My Notes
No data found.
Change Language + English
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Estimation of Working Capital Lecture 1
Estimation of Working Capital Lecture 2
Estimation of Working Capital Lecture 3
Money Market Lecture 254
Money Market Lecture 255
Money Market Lecture 256
International Trade Lecture 257
International Trade Lecture 258
International Trade Lecture 259
Terms And Conditions
84749473837373
Random text fifjfofifofjfkfkf
';
$subst = "";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
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