[+/-] : Using a Non-Capturing Group in a Regular Expression

By default, a group captures text (see Capturing Text in a Group in a Regular Expression). In some cases, a group is needed but there is no need to capture the text. A non-capturing group should be used to improve performance. A non-capturing group starts with (?:.

    String inputStr = "abbabcd";
    String patternStr = "(a(?:b*))+(c*)";
    // (?:b*) is a non-capturing group
    
    // Compile and use regular expression
    Pattern pattern = Pattern.compile(patternStr);
    Matcher matcher = pattern.matcher(inputStr);
    boolean matchFound = matcher.find();
    
    if (matchFound) {
        // Get all groups for this match
        for (int i=0; i<=matcher.groupCount(); i++) {
            String groupStr = matcher.group(i);
        }
        // group 0: abbabc
        // group 1: ab
        // group 2: c
    }

...
Read more

[+/-] : Capturing Text in a Group in a Regular Expression

A group is a pair of parentheses used to group subpatterns. For example, h(a|i)t matches hat or hit. A group also captures the matching text within the parentheses. For example, 
    input:   abbc
    pattern: a(b*)c

causes the substring bb to be captured by the group (b*). A pattern can have more than one group and the groups can be nested. For example, 
    pattern: (a(b*))+(c*)

contains three groups: 
    group 1: (a(b*))
    group 2: (b*)
    group 3: (c*)

The groups are numbered from left to right, outside to inside. There is an implicit group 0, which contains the entire match. Here is an example of what is captured in groups. Notice that group 1 was applied twice, once to the input abb and then to the input ab. Only the most recent match is captured. Note that when using * on a group and the group matches zero times, the group will not be cleared. In particular, it will hold the most recently captured text. For example, 
    input:   aba
    pattern: (a(b)*)+
    group 0: aba
    group 1: a
    group 2: b

Group 1 first matched ab capturing b in group 2. Group 1 then matched the a with group 2 matching zero bs, therefore leaving intact the previously captured b. 

Note: If it is not necessary for a group to capture text, you should use a non-capturing group since it is more efficient. For more information, see Using a Non-Capturing Group in a Regular Expression. This example demonstrates how to retrieve the text in a group.

    CharSequence inputStr = "abbabcd";
    String patternStr = "(a(b*))+(c*)";
    
    // Compile and use regular expression
    Pattern pattern = Pattern.compile(patternStr);
    Matcher matcher = pattern.matcher(inputStr);
    boolean matchFound = matcher.find();
    
    if (matchFound) {
        // Get all groups for this match
        for (int i=0; i<=matcher.groupCount(); i++) {
            String groupStr = matcher.group(i);
        }
    }

...
Read more

[+/-] : A Perl Tool To Check HTTP Proxies

Proxy Checker: only support to check http proxies.

#!/usr/bin/perl -w 
#$file:proxy_check.pl - a simple tool to check http proxy

use strict;
use LWP::UserAgent;

my $proxy_list = "/root/proxy_list.txt";
my $test_url = "http://www.mysite.com/";

print "starting...\n";

open(FD,"$proxy_list") || die "can't open file $!";

while() {
  chomp($_);
  my $proxy = $_;
  my $ua = LWP::UserAgent->new;
  $ua->timeout(20);
  $ua->proxy(['http'],$proxy);
  my $response = $ua->get($test_url);

  if ($response->is_success) {
     print "(Yes) $proxy\n";
  }
}

proxy_list.txt: http://200.69.106.161:80 http://200.208.228.52:3128 http://202.143.133.194:8080 http://201.54.163.158:6588 http://201.56.115.242:8080...
Read more

[+/-] : Perl Telnet Program

A perl program code to telnet to a machine.

#!/usr/bin/perl -w
# telnet.pl - a program to telnet to a machine
# and do some stuff
use strict;
use Net::Telnet;

my $host = shift || 'server.telent.com';
my $user = shift || $ENV{USER};
die "no user!" unless $user;
my($pass, $command);
print 'Enter password: ';
system 'stty -echo';
chop($pass = );
system 'stty echo';
print "\n";
my $tn = new Net::Telnet(Host => $host)
     or die "connect failed: $!";
$tn->login($user, $pass)
     or die "login failed: $!";
print 'Hostname: ';
print $tn->cmd('/bin/hostname'), "\n";
my @who =  $tn->cmd('/usr/bin/who');
print "Here's who:\n", @who, "\n";
print "\nWhat is your command: ";
chop($command = );
print $tn->cmd($command), "\n";
$tn->close or die "close fail: $!";

...
Read more

[+/-] : Regular Expression Search Program Example code

This example demonstrates how to use a regular expression to find matches in a string.

import java.util.regex.*;

public class BasicMatch {
    public static void main(String[] args) {
        // Compile regular expression
        String patternStr = "b";
        Pattern pattern = Pattern.compile(patternStr);

        // Determine if pattern exists in input
        CharSequence inputStr = "a b c b";
        Matcher matcher = pattern.matcher(inputStr);
        boolean matchFound = matcher.find();    // true

        // Get matching string
        String match = matcher.group();         // b

        // Get indices of matching string
        int start = matcher.start();            // 2
        int end = matcher.end();                // 3
        // the end is index of the last matching character + 1

        // Find the next occurrence
        matchFound = matcher.find();            // true
    }
}

...
Read more