Let's say you have the following Perl script.

#!/usr/bin/perl
use strict;
use warnings;

my $greeting = "Hello World\n\n";
print "greeting = $greeting";

Running this script should return the following, where there is an empty line.

[john.doe@localhost ]$ perl ~/testing.pl
greeting = Hello World

[john.doe@localhost ]$

Almost always, chomp is used to remove trailing new lines from a variable. 

#!/usr/bin/perl
use strict;
use warnings;

my $greeting = "Hello World\n\n";
chomp $greeting;
print "greeting = $greeting";

And now when the script is run, there is no empty line.

[john.doe@localhost ]$ perl ~/testing.pl
greeting = Hello World
[john.doe@localhost ]$

The following character is used to represent a new line.

\n

On the other hand, let's say you have a variable where the new line is not at the end. In this scenario, chomp would not remove the new line.

#!/usr/bin/perl
use strict;
use warnings;

my $foo = "Line 1 \n Line 2";
chomp $foo;
print "foo = $foo";

This command will replace new lines with a comma.

$foo =~ s|\n|,|g;

Now, when you print $foo, the following should be displayed.

Line 1,Line 2

It's also probably a good idea to also do something with carriage returns.

$foo =~ s|\r\n|,|g;

And here is how you can replace new lines with the literal new line character \n.

$foo =~ s|\r\n|\\n|g;

Which should produce the following.

Line 1\nLine 2