use strict;
use warnings;
my $text = <<EOT;
I probably do not understand your 
requirement.  Is it not as simple 
as reading the file line by line, 
removing all newlines and adding a 
newline after all full stops, question 
and exclamation marks?  After that 
operation each line is one sentence.
EOT
open my $fn, "<", \$text;
while(<$fn>){
		chomp;
		s/[.!?]\K\s*/\n/g;
		print;
}
close $fn;