Regex to match . (periods marking end of sentences) but not Mr. (as in Mr. Hopkins)

Question

I'm trying to parse a text file into sentences ending in periods, but names like Mr. Hopkins are throwing false alarms on matching for periods.

What regex identifies "." but not "Mr."

For bonus, I'm also using ! to find end of sentences, so my current Regex is /(!/./ and I'd love an answer that incorporates my !'s too.

Answer 1

Use negative look behind.

(?<!Mr|Mrs|Dr|Ms)\.

This will match a period only if it does not come after Mr, Mrs, Dr or Ms

<?
   $str = "This is Mr. Someone and Mrs. Somebody. They are here to meet Dr. SomeoneElse.";
   $str = preg_replace("/(?<!Mr|Mrs|Dr|Ms)\\./", "\n", $str);
   echo($str);
?>
//outputs:
This is Mr. Someone and Mrs. Somebody
 They are here to meet Dr. SomeoneElse

Answer 2

This can't be done with any simple mechanism. It's hopelessly ambiguous. Sentences can end with abbreviations, and in those cases they aren't written with two periods.

See Unicode TR29. Also see the ICU open source library, which includes a basic implementation.

Answer 3

Are your sentences always followed by two spaces? If so you could just check for that...

/\.\s{2}/

and incorporating other end of sentence punctuation: /[\.\!\?]\s{2}/

You could also check other things which could be indicators of the end of a sentence, like if the next word is capitalized, is it followed by a carriage return, etc. But at best you'll just be able to make an educated guess, as pointed out above the period is just too ambiguous.