#!/usr/bin/perl

use strict;
use warnings;

my $text = "start \\chapter{hello}\n end\n";

my $patternreadfromfile = <DATA>;
chomp $patternreadfromfile;

my $inpattern = qr/\\chapter\{(.*)\}/;

eval "\$text =~ s/$inpattern/$patternreadfromfile/g";

print "$text\n";

__DATA__
-- FOUND $1 --