Re: Validate Ip address Regexp

Regular expression is the wrong approach IMHO. The IPv4 address consists of four bytes (0..255) separated by dots.
Have a loock at split and pack. If you pack the byte values and unpack them again and assemble the IP string, origin and result should be equal if the origin is a valid IP address.

print "Enter IP Address:";
chop(my $ip = <STDIN>);
my $parsed = join'.', unpack "C4", pack "C4", split/\./, $ip;
if ($parsed eq $ip) {
    print "yes match $parsed\n";
} else {
    print "no match: parsed $parsed <> input $ip\n";
}
[download]

This of course doesn't work for IP addresses written with leading zeroes e.g 001.012.013.225 - which I consider bad practice anyways, because in my book a leading zero marks an octal value.

If you want to be absolutely sure, you can isolate the four bytes with a regular expression limiting each string representation to 3 chars of type number, i.e (\d{3]), then run the four values through pack/unpack as described above. There are many other ways to do this task...

perl -le'print map{pack c,($-++?1:13)+ord}split//,ESEL'

Comment on Re: Validate Ip address Regexp Select or Download Code

Replies are listed 'Best First'.
Re^2: Validate Ip address Regexp by Laurent_R (Canon) on Nov 28, 2015 at 22:53 UTC
Regular expression is the wrong approach IMHO. Well, quite possibly, but the OP wanted to practice regular expressions (which is why I gave a pure regex solution) and, besides, using split is in fact using regular expressions. But I agree that checking for numbers in the 0-255 range with a pure regex is somewhat unwieldy. An easier way might be something along these lines: `print "Valid IP\n" if 4 == grep { /^\d+$/ and $_ < 256 } split /\./, $ +ip;` [download] (although this is still not entirely satisfactory, since this would validate something like "23.45.aa3.234.244"", so a bit more effort might be needed). Note that Perl 6's regexes allow a code assertion to be inserted within a regex, leading for example to something like this: `my regex octet {(\d 1..3) <?{0 <= $0 <= 255 }> } my regex ip {^ <octet> 4 % '.' $}` [download]	[reply] [d/l] [select]

Replies are listed 'Best First'.

Re^2: Validate Ip address Regexp
by Laurent_R (Canon) on Nov 28, 2015 at 22:53 UTC

Regular expression is the wrong approach IMHO.

split

But I agree that checking for numbers in the 0-255 range with a pure regex is somewhat unwieldy. An easier way might be something along these lines:

print "Valid IP\n" if 4 == grep { /^\d+$/ and $_ < 256 } split /\./, $
+ip;
[download]

Note that Perl 6's regexes allow a code assertion to be inserted within a regex, leading for example to something like this:

my regex octet {(\d ** 1..3) <?{0 <= $0 <= 255 }> }
my regex ip {^ <octet> ** 4 % '.' $}
[download]

[reply]
[d/l]
[select]