#!/usr/bin/perl

use strict;

my $Usage = "Usage: $0 filename.txt > fixed.txt\n";
die $Usage unless ( @ARGV == 1 and -f $ARGV[0] );

$/ = '';  # empty string means blank lines mark end-of-record (cf. perldoc perlvar)

my @pars = <>;  # read all paragraphs into @pars

my $sterm = qr/[.!?][)"']*/;  # regex for end-of-sentence

for ( my $i = 0; $i < $#pars; $i++ )  # skip last paragraph
{
    next if ( $pars[$i] =~ /$sterm\s*$/ );

# get here when paragraph ends in mid-sentence

    my $j = $i + 1;  # refer to next par for tail part of sentence
    ( my $tail ) = ( $pars[$j] =~ /(.*?$sterm)\s*/ );
    $pars[$i] =~ s/\s*$/ $tail\n\n/; # add tail to current par
    $pars[$j] =~ s/\Q$tail\E\s*//; # remove it from next par
}

print @pars;