G'day jwkuo87,

Welcome to the monastery.

The following technique uses paragraph instead of slurp mode (see $/ in perlvar: Variables related to filehandles). This gets around matching Chapter 2 in the TOC.

I've also used the '..' range operator (which davido showed earlier).

Finally, we stop reading the input file as soon as Chapter 3 is found.

Here's the code. Note that, for testing purposes, I've added a second (dummy) paragraph to Chapter 2 and truncated the existing first paragraph.

#!/usr/bin/env perl

use strict;
use warnings;

{
    local $/ = '';

    while (<DATA>) {
        next unless /^Chapter 2/ .. /^Chapter 3/;
        last if /^Chapter 3/;
        print;
    }
}

__DATA__
Table of Contents
Chapter 1. Introduction
Chapter 2. Main
Chapter 3. Conclusion

==============================

Chapter 1. Introduction
This is the introduction preceding Chapter 2.

Chapter 2. Main
This is the text contained in Chapter 2 and will ...

Assume more than one paragraph.

Chapter 3. Conclusion
This is the conclusion.
[download]

Output:

Chapter 2. Main
This is the text contained in Chapter 2 and will ...

Assume more than one paragraph.
[download]