You have to remove all white space from the beginning and end of each line. Then if a line break follows a character that is not an end of line (.?!), it is replaced with a space.

EDIT: Oops, forgot the g flag,and also forget to mask out \n itself. Fixed the problem.

EDIT: Oops again. I really must have been tired when I wrote this! As jwest points out via PM, I was only removing white space from the beginning OR end of the lines, not both at the same time. Fixed the problem.

use strict;
use warnings;

@_ = <DATA>;
s/^\s+|\s+$//g for @_;
$_ = join "\n", @_;
##### END OF LINE MARKERS
s/([^\.\?!\n])\n+/$1 /g;
##### ADD TO AS NECESSARY
print;

__DATA__
This line breaks

in the middle.

This one doesn't.
Neither does this!
Or this?

I hope.
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