use strict;
use warnings;
use Getopt::Long qw(:config no_ignore_case);
use Pod::Usage;

my %opt;
my ( $opt_help, $opt_man, $opt_versions );

GetOptions(
[...]
    'P|password=s'      => \$opt{Pass},
[...]
    's|snmp=s'          => \$opt{snmp},
[...]
    'username=s'        => \$opt{user},
[...]
    'help!'             => \$opt_help,
    'man!'              => \$opt_man,
    'versions!'         => \$opt_versions
) or pod2usage( -verbose => 0 );

if ( defined $opt_help ) {
    pod2usage( -verbose => 99, -sections => "OPTIONS/PASSWORD MODE" )
      if defined $opt{Pass};
    pod2usage( -verbose => 99, -sections => "OPTIONS/SNMP MODE" )
      if defined $opt{snmp};
    pod2usage( -verbose => 99, -sections => "OPTIONS/TELNET SSH MODE" )
      if ( defined $opt{user} or defined $opt{pass} );
}

pod2usage( -verbose => 1 ) if defined $opt_help;
pod2usage( -verbose => 2 ) if defined $opt_man;

[...]

__END__

=head1 NAME

[...]

=head1 SYNOPSIS

[...]

=head1 DESCRIPTION

[...]

=head1 OPTIONS

[...]

=head2 PASSWORD MODE

To activate B<Password Mode>, use the -P option.

[...]

=head2 SNMP MODE

To activate B<SNMP Mode>, use the -s option.

[...]

=head2 TELNET SSH MODE

To activate B<Telnet Mode>, use the -p option without -s.

[...]

=cut