...
use strict;
use Getopt::Std;

use vars qw/ $opt_i $opt_s $opt_c $opt_h /;

sub usage () {
     my $msg = shift || "-h prints this message";
     print "$msg\nusage:$0 -i<ip addr> -s<tftp server> -c<config file>\n";

}


getopts( 'i:s:c:h' );

if ( !$opt_i ) {
    usage( "Please specify ip address" ); 
    exit 1;
}
if ( !$opt_s ) {
    usage( "Please specify  tftp server" ); 
    exit 1;
}
if ( !$opt_c ) {
    usage( "Please specify config file" ); 
    exit 1;
}

if ( $opt_h ) {
    usage;
    exit 0;
}

...