diamondsandperls has asked for the wisdom of the Perl Monks concerning the following question:

I need to subtract one digit from the last octet of the first ip and i need to add one to the last octet of the second ip address.

I am obviously struggling with this as my current code will dictate.

SAMPLE STRING: 192.168.1.1-192.168.1.254 needs to be 192.168.1.0-192.168.1.255

I have many strings of text that are random but the format is similar but the sample string can be 172.15.29.21-172.15.30.23 needs to be 172.15.29.20-172.15.30.24. These are all made up. In the first octet there will never be a zero as the last digit so only the very last digit in the octet needs to be regexed and subracted.

#!C:/Perl/bin/perl.exe

use strict;
use warnings;

my $ip_1 =~ m/(\d)-/g;
    $ip_1 = int($ip_1);

my $ip_2 = $ip_1 - 1;

my $input_file = 'CrystalReportViewer1.csv';
my $output_file = 'CrystalReportViewer2.csv';

    open(my $output_fh, '>', $output_file)
        or die "Failed to open $output_file - $!";
        
    open(my $input_fh, '<', $input_file)
        or die "Failed to open $input_file: $!";

    while ( <$input_fh> ) {
            s/$ip_1/$ip_2/;
            
            
            print {$output_fh} $_;
        }
    
    close $output_fh;

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Replies are listed 'Best First'.
Re: replacing the last portions of an octet
by blue_cowdawg (Monsignor) on Sep 18, 2012 at 19:40 UTC

    Something like this? 

    #!/usr/bin/perl -w
use strict;

my $ips='192.168.1.1-192.168.1.254';

my ($first,$second)=split('-',$ips);
printf "%s-%s\n",$first,$second;
$first = incip($first);
$second = incip($second);

printf "%s-%s\n",$first,$second;

exit(0);

sub incip {
    my $ip=shift;
    my @o=split(/[\.]/,$ip);
    $o[3]++;
    return sprintf("%d.%d.%d.%d",@o);

}

    [download]

    Peter L. Berghold -- Unix Professional
    Peter -at- Berghold -dot- Net; AOL IM redcowdawg Yahoo IM: blue_cowdawg
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[d/l]
      sorry just noticed those are subroutines ill play around some more
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      thanks was able to play around with your sample code to get what i was looking for thanks for the heads up and insight
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Re: replacing the last portions of an octet
by atcroft (Abbot) on Sep 18, 2012 at 20:37 UTC

    Here were two functions I wrote (before I found out about things like Net::IP or NetAddr::IP that you might find helpful: 

    sub dq2number { 
    my $ip = shift; 
    return unpack "N", pack "C4", split /\D/, $ip; 
} 
sub number2dq { 
    my $n = shift; 
    return join q{.}, unpack "C4", pack "N", $n; 
}

    [download]

    Here is an example, so you can see the result 

    use strict;
use warnings;

my @c = qw/
  0.0.0.0  
  0.255.255.255 
  10.0.0.1 
  172.16.0.1 
  127.0.0.1 
  192.168.0.1
  /; 
foreach my $d (@c) { 
    print $d, q{ }, 
      number2dq( dq2number( $d ) - 1 ), q{ }, 
      number2dq( dq2number( $d ) + 1 ), qq{\n}; 
}
sub dq2number { 
    my $ip = shift; 
    return unpack "N", pack "C4", split /\D/, $ip; 
} 
sub number2dq { 
    my $n = shift; 
    return join q{.}, unpack "C4", pack "N", $n; 
}
# Output:
# 0.0.0.0 255.255.255.255 0.0.0.1
# 0.255.255.255 0.255.255.254 1.0.0.0
# 10.0.0.1 10.0.0.0 10.0.0.2
# 172.16.0.1 172.16.0.0 172.16.0.2
# 127.0.0.1 127.0.0.0 127.0.0.2
# 192.168.0.1 192.168.0.0 192.168.0.2

    [download]

    Hope that helps.

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[d/l]
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Re: replacing the last portions of an octet
by Kenosis (Priest) on Sep 18, 2012 at 20:14 UTC

    Here's another option:

    use Modern::Perl;

my $IPs =  '192.168.1.1-192.168.1.254';
$IPs =~ s/(.+\.)(\d+)(\s*-\s*.+\.)(\d+)/$1 . ($2 - 1) . $3 . ($4 + 1)/
+e;
say $IPs;

    [download]

    Output:

    192.168.1.0-192.168.1.255

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Re: replacing the last portions of an octet
by AnomalousMonk (Archbishop) on Sep 19, 2012 at 02:27 UTC

    An example using the IP decimal octet regex from Regexp::Common's friend Regexp::Common::net: 

    >perl -wMstrict -le
"use Regexp::Common qw(net);
 ;;
 my $s = shift;
 print qq{'$s'};
 ;;
 $s =~ s{ \b ($RE{net}{IPv4}) - ($RE{net}{IPv4}) \b }
        { add_oct($1, -1) . '-' . add_oct($2, +1)   }xmse;
 print qq{'$s'};
 ;;
 sub add_oct {
   (my $ip = $_[0]) =~ s{ (\d+) \z }{ ($1 + $_[1]) & 0xff }xmse;
   return $ip;
   }
"  "192.168.1.1-192.168.1.255"
'192.168.1.1-192.168.1.255'
'192.168.1.0-192.168.1.0'

    [download]
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[d/l]
Re: replacing the last portions of an octet
by ksublondie (Friar) on Sep 18, 2012 at 19:57 UTC
    ...You'll probably need to test that the last number in each octet is 0 <= x <= 255 after the arithmetic...
[reply]
      good point this will not be needed as none of the numbers ever are this however the first ip needs to decrease and the sample code increases both how do i decrease a wild guess was decip but that did not work
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