The $ character is used to do something from the end of a line. For example, let's say the $foo variable contains "Hello".

my $foo = "Hello";

The $ character can be used to append to the $foo variable. In this example, "World" is appended to the end of the $foo variable.

$foo =~ s|$| World|;

Printing $foo . . .

print $foo;

Should return "Hello World".

Hello World

The $ character can also be used to replace. In this example, the $foo variable will be replaced to be "Hello Earth".

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

my $foo = "Hello World";
$foo =~ s|World$|Earth|;

Often, a variable may contain multiple different strings. Let's say sometimes the $foo variable will end with "World" and sometimes "Earth". Here is how you would update the $foo variable to end with "bar" instead of World or Earth.

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

my $foo = "Hello World";
$foo =~ s|(World|Earth)$|bar|;