vasanth.easyrider has asked for the wisdom of the Perl Monks concerning the following question:

Hi Perl Monks

i have a perl script

#!/usr/bin/perl

use strict;
use warnings;

my $output = "ae4.5784     up    down inet     182.75.123.121/30";
if($output =~ m/(\d{1,3}\.\d{1-3}\.\d{1-3}\.\d{1-3})$/g)
{
    print "There is an IPdressAd in the output string\n";
}
else
{
    print "There is no IPAddress in the output string";
}

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My requirement is to check if $output has an IPaddress in it or not. In above example - it contains an IP.
how to give the correct regular expression . The regular expression i have given is not working

Replies are listed 'Best First'.
Re: IPAddress check (updated)
by haukex (Archbishop) on Mar 13, 2018 at 11:46 UTC

    "is not working" is not really an adequate problem description. Please see I know what I mean. Why don't you?

    But take a look at your regular expression: \d{1,3} vs. \d{1-3} - why the difference? One is right, the other is wrong. See perlrequick and perlretut.

    Note that even if you fix that, the regular expression will still match invalid IP's like 999.999.999.999. Instead of reinventing the wheel, I'd recommend Regexp::Common::net:

    use warnings;
use strict;
use Regexp::Common qw/net/;

my $output = "ae4.5784     up    down inet     182.75.123.121/30";

if ( $output =~ /\b$RE{net}{IPv4}\b/ ) {
    print "There IS an IPAddress in the output string\n";
}
else {
    print "There is NO IPAddress in the output string\n";
}

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    Update: Added the word boundary \b to the above regex, because otherwise it would have matched something like 1111.1.1.1 (because 111.1.1.1 is a valid IP) or 256.255.255.256 (because 56.255.255.25 matches).

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Re: IPAddress check
by thanos1983 (Parson) on Mar 13, 2018 at 11:48 UTC

    Hello vasanth.easyrider,

    This question has been asked again Validate Ip address Regexp. I would use a module such as Regexp::Common.

    Sample of code from the Validate Ip address Regexp given by neilwatson

    #!/usr/bin/perl
use strict;
use warnings;
use Regexp::Common qw/ net /;

my $output = "ae4.5784     up    down inet     182.75.123.121/30";
if ( $output =~ m/$RE{net}{IPv4}/ ){
    print "match!\n"
}

__END__

$ perl test.pl
match!

    [download]

    Update: See update of fellow Monk haukex above for the correct usage.

    Hope this helps, BR.

    Seeking for Perl wisdom...on the process of learning...not there...yet!
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      Please note haukex's Update here about using a boundary assertion of some kind. The raw regex  $RE{net}{IPv4} used in the code example here matches the string
          my $output = "ae4.5784     up    down inet     99999.75.123.99999/30";
      which is problematic for containing a valid IP.

      Give a man a fish:  <%-{-{-{-<

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        Hello AnomalousMonk,

        Thank you for this minor but important notice. :)

        BR / Thanos

        Seeking for Perl wisdom...on the process of learning...not there...yet!
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