I think this is a pretty good IP sanity check snippet. If anyone has any comments please let me know!
use strict;

{ package IPSanity;

    use Socket;
    sub VerifyIP {
        chomp ($_);
        my ($a,$c,$d,$e,$f,$g);
        my $b = 0;
        if ($_ =~ /[a-zA-Z]+/) {
            print "$_\n";
            $_ = gethostbyname($_);
            ($c,$d,$e,$f) = unpack('C4', $_);
            $_ = $c . "." . $d . "." . $e . "." . $f;
        }
        
        my @_temp = split(/\./,$_);
        
        $g = $#_temp;
        undef $_;
        
        if ($g ne '3') {
            print "Your IP address is malformed.  I hope this isn't a 
+reflection of the user...\n";
            exit;
        }
    
        foreach $a(@_temp) {
            if ($a =~ /\b\d\b|\b\d\d\b|\b\d\d\d\b/) {
                if ($a >= 0 && $a <= 255) {
                    $_ = $_ . int($a);
                    $_ = $_ . "." unless ($b > 2);
                    $b++;
                }
            }
        }
        
        my $_IP = inet_aton( $_ );
        length($_IP) or die "Sorry, '$_' is invalid.\n";
        $_IP = inet_ntoa($_IP);
        print "$_IP is valid\n";
    }
}


print "IP or Domain Name: ";
$_ = <>;
chomp;
IPSanity->VerifyIP($_);

[download]

Replies are listed 'Best First'.
Re: IP Sanity Check
by grinder (Bishop) on Nov 11, 2002 at 20:39 UTC

    Note that it is perfectly valid to omit the penultimate zero value octets. You can play around with this in the following one-liner:

    % perl -MSocket -e 'print inet_aton shift' 65.0.0.65|hexdump
0000000 0041 4100
0000004
% perl -MSocket -e 'print inet_aton shift' 65.65|hexdump
0000000 0041 4100
0000004

    [download]

    That is, there exists a shorthand for x.0.0.y and x.y.0.z (but not x.0.y.z). To complete the picture, you can also do this for 0.0.0.x, but that's hardly ever useful.

    Which is another reason why inet_aton is such a good idea.

    <update> Re your 01.1.1.010 problem, there is an issue you should be aware of. A leading 0 in a string, signals octal (assuming you're trying to interpret the string as a number). Consider the following: 

    % perl -MSocket -le 'print inet_ntoa inet_aton shift' 01.1.1.10
1.1.1.10
% perl -MSocket -le 'print inet_ntoa inet_aton shift' 01.1.1.010
1.1.1.8

    [download]

    Note that I don't see the behaviour you describe, although I'd be loathe to consider this the work of an interfering shell. If this is really a problem, I'd be inclined to do a simple cleanup prior to calling inet_aton with something like (untested):

    my $_IP = inet_aton( join '.',
    map { s/^0([1-9]\d*)$/$1/; $_ } # strip leading zeroes
    split( /\./, $original_ip)      # of each octet
);

    [download]
    </update>
    print@_{sort keys %_},$/if%_=split//,'= & *a?b:e\f/h^h!j+n,o@o;r$s-t%t#u'
[reply]
[d/l]
[select]
      the reason why i am doing it the way i am is so that an IP address that somehow gets to the system like '01.1.1.010' is successfully resolved to '1.1.1.10'. If you pass that to inet_aton directly I get (at least on this system with activestate perl version 5.6) 0.1.1.0.

      I hope I am not doing something utterly stupid...

      ; )

      www.loungeman.com
[reply]
Re: IP Sanity Check
by jupe (Beadle) on Nov 11, 2002 at 18:50 UTC
    Oh yeah, mega props to jdporter for being a perl guru and all around nice guy (pointed me to the inet_aton for actually verifying the address).
[reply]

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