Regex to remove single characters from string

Question

Consider the following strings

breaking out a of a simple prison
this is b moving up
following me is x times better

All strings are lowerca

Answer 1

As a one-liner:

$result = preg_replace('/\s\p{Ll}\b|\b\p{Ll}\s/u', '', $subject);

This matches a single lowercase letter (\p{Ll}) which is preceded or followed by whitespace (\s), removing both. The word boundaries (\b) ensure that only single letters are indeed matched. The /u modifier makes the regex Unicode-aware.

The result: A single letter surrounded by spaces on both sides is reduced to a single space. A single letter preceded by whitespace but not followed by whitespace is removed completely, as is a single letter only followed but not preceded by whitespace.

So

This a is my test sentence a. o How funny (what a coincidence a) this is!

is changed to

This is my test sentence. How funny (what coincidence) this is!