You're not a million miles away!

Pass your data to new() (the constructor) as a hash ref.

#!/bin/perl5

use strict;
use warnings;
use Data::Dumper;

#use lib '/home/nhwatson/lib/perl/';
use Mine::Openview::opcmsg;

my $ovs = Mine::Openview::opcmsg->new(
 {
    msg => 'This is a test',
    app => 'Perl script',
    obj => 'Perl module',
    sev => 'warning',
    msgg => 'message group',
    ser => 'service ID',
  }
);

#die Dumper $ovs;

my $return = $ovs->send;

print "\nreturn = " . $return . "\n";
[download]

Your send method can then get the data from the object.

package Mine::Openview::opcmsg;

use strict;
use warnings;

sub new {
    my $class = shift;
    my $self  = shift;
    return bless $self, $class;
}

sub send {
  
  my $self = shift;

  my $cmd = join "\n",
    "opcmsg",
    "msg_text = " . $self->{msg},
    "application = " . $self->{app},
    "object = " . $self->{obj},
    "severity = ".$self->{sev},
    "msg_grp = " . $self->{msgg},
    "service_id = " . $self->{ser};
  
  return $cmd;
}

1;
[download]

output:

---------- Capture Output ----------
> "C:\Perl\bin\perl.exe" monk.pl

return = opcmsg
msg_text = This is a test
application = Perl script
object = Perl module
severity = warning
msg_grp = message group
service_id = service ID

> Terminated with exit code 0.
[download]

As dorward suggested above, have a look at the docs.