$re = '/(?m)^Computer\r?\n.+\r?\n(?:fPromptForPassword|AllowLocalPolicyMerge|AllowLocalIPsecPolicyMerge)\r?\n.+(?:\r?\n)?/mi';
$str = 'one
---
Computer
Software\\Policies
fPromptForPassword
DWORD:1
---
two
---
Computer
Software\\Policies
AllowLocalIPsecPolicyMerge
DWORD:1
---
three
';
preg_match_all($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