my $sshport;
my $errorstate = 0;

print "\n Please Enter Custom port for SSH server:\n";
chomp($sshport = <STDIN>);
while (!$errorstate) {
    if ($sshport =~  /^[1-9]\d{1,9}$/ ) {
        $errorstate = 1;
    } else {
        print " Please Enter valid ssh port number:\n";
        chomp($sshport = <STDIN>);
    }
}

open (SSHD_CONFIG,'sshd_config') or die ("Could not able to open the file $!");
open (SSHD_CONFIG_NEW,">",'sshd_config.new') or die ("Could not create the new file $!");

while (<SSHD_CONFIG>){
 if (/^port/i) {
    s/Port.+/Port $sshport/;
 } elsif (/^#port\s/i) {
    s/#Port.+/Port $sshport/;
 }
 print SSHD_CONFIG_NEW $_;
}

rename('sshd_config','sshd_config.old');
rename('sshd_config.new','sshd_config');