how to write script usage sub routine for the perl file?

[perlanswers]

How can i write the usage function to run the file in perl.

./html.pl -root="/home/data/multiple/" -out="/home/data/output" -file=
+"/home/data/file.txt"

I have the above perl file.I have to run the same file in the terminal as i mentioned above.How can i include usage of the script inside the perl file.
code which i have tried

use strict;
use warnings;
use Getopt::Long qw(GetOptions);
sub usage {
   if (@_) {
      my ($msg) = @_;
      chomp($msg);
      print(STDERR "$msg\n");
   }

GetOptions(
       'root=s' => \my $dir,
    'out=s' => \my $out,
    'file=s' => \my $file,
)
    or usage();