Using variable to hold regex expression

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

I am trying to use variables to hold the regex exppression to make it easier to code, and I'm running into one issue parsing firewall logs.

When I call the same regex variable multiple times the first group returns the correct result but the second one shows part of the first IP address.

-- Sample data Mar 10 07:42:38 DR-FW-1 : %ASA-6-305011: Built dynamic UDP translation from inside:172.28.17.130/3324 to outside(internet-traffic):69.176.102.83/24295

output: 
re1  ->  172.28.17.130
re2  ->  17.

------------------------------------------

my $Raw_Log = "";
my $re_ipv4 = qr/(([2]([0-4][0-9]|[5][0-5])|[0-1]?[0-9]?[0-9])[.]){3}(
+([2]([0-4][0-9]|[5][0-5])|[0-1]?[0-9]?[0-9]))/;
# Open file to read lines
my $logfile = $ARGV[0];
my $linenum = 0;

open(LOGFILEHD, $logfile);

while( <LOGFILEHD>){
   $Raw_Log = $_;
   print "$Raw_Log\n";
   $Raw_Log =~ /($re_ipv4).*($re_ipv4)/;

   print "re1  ->  $1\n";
   print "re2  ->  $2\n";

   $linenum  += 1;
}
close(LOGFILEHD);
[download]

Comment on Using variable to hold regex expression Download Code

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Re: Using variable to hold regex expression by choroba (Cardinal) on Mar 11, 2013 at 23:12 UTC
`$1` Corresponds to the first opening capturing parenthesis, `$2` corresponds to the second one. You probably want to use `$5` instead of `$2` - let us count: `((([2]([0-4][0-9]\|[5][0-5])\|[0-1]?[0-9]?[0-9])[.]){3}(([2]([0-4][0-9]\| +[5][0-5])\|[0-1]?[0-9]?[0-9]))).*( 123 4 56 7` [download] لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ	[reply] [d/l] [select]
Re: Using variable to hold regex expression by Kenosis (Priest) on Mar 11, 2013 at 23:36 UTC
Have you considered using Regexp::Common::net to capture those IPs? use strict; use warnings; use Regexp::Common qw/net/; while (<DATA>) { if ( my ( $firstIP, $secondIP ) = /($RE{net}{IPv4})/g ) { print "FirstIP: $firstIP\nSecondIP: $secondIP\n\n"; } } __DATA__ Sample data Mar 10 07:42:38 DR-FW-1 : %ASA-6-305011: Built dynamic UDP + translation from inside:172.28.17.130/3324 to outside(internet-traff +ic):69.176.102.83/24295 Sample data Mar 10 07:42:38 DR-FW-1 : %ASA-6-305011: Built dynamic UDP + translation from inside:155.0.42.42/3324 to outside(internet-traffic +):71.200.20.7/24295 [download] Output: `FirstIP: 172.28.17.130 SecondIP: 69.176.102.83 FirstIP: 155.0.42.42 SecondIP: 71.200.20.7` [download]	[reply] [d/l] [select]
Re^2: Using variable to hold regex expression by salatconed (Initiate) on Mar 12, 2013 at 00:05 UTC
Perhaps using IP addresses was not a good example, I'm trying to figure out how to parse a string which has repetitive data, so I can write the regex expression once and get multiple returns if they exist the same way your code got both IP addresses in one call.	[reply]
Re^3: Using variable to hold regex expression by AnomalousMonk (Archbishop) on Mar 12, 2013 at 00:35 UTC
... how to parse a string which has repetitive data ... As choroba pointed out, every `(pattern)` pair of parentheses in a regex captures something (even undef possibly) to its corresponding capture variable. One way to parse a string using nested regexes is avoid using a gazillion capturing groups. Use the non-capturing `(?:pattern)` instead for grouping. See perlre, perlrequick, perlretut. In the IP example (but this should generalize to any repetitive data you wish to extract): `>perl -wMstrict -le "my $decimal_octet = qr{ 2 (?: [0-4] \d \| 5 [0-5]) \| [01]? \d? \d }xms; my $ip = qr{ (?<! \d) $decimal_octet (?: \. $decimal_octet){3} (?! \d) }xms; print $ip; ;; my $s = '123.45.6.234 xx yyy zz 000.12.34.255'; my @ips = $s =~ m{ $ip }xmsg; printf qq{'$_' } for @ips; " (?^msx: (?<! \d) (?^msx: 2 (?: [0-4] \d \| 5 [0-5]) \| [01]? \d? \d ) (? +: \. (?^msx: 2 (?: [0-4] \d \| 5 [0-5]) \| [01]? \d? \d )){3} (?! \d) ) '123.45.6.234' '000.12.34.255'` [download] Note that neither `(?:pattern)` nor the `(?<!pattern) (?!pattern)` look-around assertions capture. Indeed, nothing captures (to a capture variable) since data is extracted in list context directly to an array.	[reply] [d/l] [select]
Re^3: Using variable to hold regex expression by Kenosis (Priest) on Mar 12, 2013 at 00:31 UTC
If I'm understaing you correctly, the `my ( $firstIP, $secondIP ) = /($RE{net}{IPv4})/g` in the above code does what you've described.	[reply] [d/l]