Quick note -- it's not actually working so well yet, even disregarding abbreviations. Consider the following input:

This is a sentence. This is another sentence. This is a third
sentence, which also happens to be spanning a line. This is a
sentence as well... I think. This is an abbreviation, cf. the
list posted on Perlmonks. This is a sentence; this is the last
sentence.
[download]

This produces:

This is a sentence.
This is another sentence.
This is a thirdsentence, which also happens to be spanning a line.
This is asentence as well.
I think.
This is an abbreviation, cf.
Perlmonks.
This is a sentence;
[download]

As opposed to:

This is a sentence.
This is another sentence.
This is a third sentence, which also happens to be spanning a line.
This is a sentence as well... I think.
This is an abbreviation, cf.
the list posted on Perlmonks.
This is a sentence;
this is the last sentence.
[download]

Note how the third and fourth one are missing a space and how lowercase characters following semicolons or periods aren't handled correctly.

Try the following -- add a space in your loop, and use a lookahead assertion to take a peek at what's following a period or colon:

#!/usr/bin/perl

use feature qw/say/;
use strict;
use warnings;

my $s;
my @arr;

while(<>) {
  chomp $_;
  $s .= $_ . " ";
}
@arr = $s =~ m/[A-Z].+?[.;](?=[^.;][A-Z]|\s*$)/g;
foreach (@arr) {
    say;
}
[download]

This produces:

This is a sentence.
This is another sentence.
This is a third sentence, which also happens to be spanning a line.
This is a sentence as well...
I think.
This is an abbreviation, cf. the list posted on Perlmonks.
[download]

As you can see, it's not perfect -- it still splits if you have e.g. a run-on sentence followed by an "I", or in fact any uppercase word, e.g. a proper noun --, but it mostly handles abbreviations (arbitrary ones, even). What I'd do to fix the remaining edge cases is add another processing step after the regex where you loop over @arr, check if each element ends with a known abbreviation, and join that element with the next one if so.

Try this one on for size:

[A-Z].+?[.;](?<!\.{3})(?=[^.;][A-Z]|\s*$)

Works like a charm. BTW, I was gonna say that

m/[A-Z].+?[.;](?<!\.{2,})(?=[^.;][A-Z]|\s*$)/g
[download]

would perhaps be even better, so as to not hardcode any specific number of periods for run-on sentences, but it turns out that:

Variable length lookbehind not implemented in regex m/[A-Z].+?[.;](?<!
+\.{2,})(?=[^.;][A-Z]|\s*$)/
[download]

Sigh. (Oh well, at least there's workarounds; see Why is variable length lookahead implemented while lookbehind is not?.)

Many thanks, I tried it and it seems to work pretty well, The loop over @arr seemed to work for a couple of abbreviations. I will need to add all of them and I am sure it will work pretty decently.

substitue the newlines with spaces, otherwise

this is line one
rous is the first word of line two
[download]

will become

which is not what you want

open my $fh, "<", "test" or die "test: $!"
while (<$fh>) {
    chomp;
    $s .= " $_";
    }
[download]

or shorter

Or even shorter

TIMTOWTDI - chomp in a map and join seems fairly concise yet readable.

$ perl -Mstrict -Mwarnings -E '
open my $inFH, q{<}, \ <<EOD or die $!;
Line 1
Line 2
Line 3
EOD

my $wholeText = join q{ }, map { chomp; $_ } <$inFH>;

say $wholeText;'
Line 1 Line 2 Line 3
$
[download]

I hope this is of interest.

Cheers,

JohnGG

You can also add your own items to the list like this:

use Lingua::EN::Sentence qw( get_sentences add_acronyms );
 
add_acronyms('ed','eds');  # adding support for 'Ed. Eds.'
my $sentences = get_sentences($text);
for my $sentence (@$sentences) {
    # do something with $sentence
}
[download]

Is it just me or doesn't anybody else read this like a homework assignment? I mean...how can you have a ready-made list of abbreviations...a fairly complete one mind you, but have no idea how to integrate into a script?

Sorry. I am a newbie but rather old to do homework assignment: I am 65 years old and work on language analysis and am learning Perl since it helps me do a lot of string manipulation which in C would be an expensive proposition. No homework assignment here, I am afraid. Sentence splitting is a major problem in NLP and creates issues which you can see from the replies posted.

Never too old for school or homework. The whole world is a school.

The linked module doesn't handle abbreviations.
لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ

choroba: The linked module doesn't handle abbreviations.

abbrev -> Text::UnAbbrev - Expand abbreviations and acronyms.

sentence -> Lingua::Sentence - Perl extension for breaking text paragraphs into sentences