In this example, the $foo variable contains "Hello World".

my $foo = "Hello World";

The lc (lower case) operator can be used to update the value to be "hello world".

$foo = lc($foo);

In a regular expression, the i operator can be used to ignore case in a comparison. In this example, the comparison operator checks if the $foo variable contains the text "hello", regarless of the case sensitivity of the value in the $foo variable.

if ($foo =~ /hello/i) {
  print "foo contains hello\n";
}