$re = '/(,\s(?:vol|pt)\.(*SKIP)(*F)|(?:vol|pt|volume|part))/im';
$str = 'Should Match:
a) Any occurences of "Volume" OR "Part" (Case Insensitive);
b) Any occurence of "vol" or "pt" (CI) that does not have [[comma][space] before AND [period] after;
My volume 1
My name vol2.
My, volume 1
, pt. vol2.
, part.
, pt.
, pt
, vol
. pt.
// Should match below as there is no [period] after it
The Red Pill, Pt 2
, Pt 2';
$subst = "\1";
$result = preg_replace($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