Open HTTP port 80 on CentOS

Got from here.

1. Look at the current iptables
# iptables --line -vnL
Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
num   pkts bytes target     prot opt in     out     source               destination
1        0     0 ACCEPT     udp  --  virbr0 *       0.0.0.0/0            0.0.0.0/0           udp dpt:53
2        0     0 ACCEPT     tcp  --  virbr0 *       0.0.0.0/0            0.0.0.0/0           tcp dpt:53
3        0     0 ACCEPT     udp  --  virbr0 *       0.0.0.0/0            0.0.0.0/0           udp dpt:67
4        0     0 ACCEPT     tcp  --  virbr0 *       0.0.0.0/0            0.0.0.0/0           tcp dpt:67
5     195K  212M ACCEPT     all  --  *      *       0.0.0.0/0            0.0.0.0/0           state RELATED,ESTABLISHED
6        3   252 ACCEPT     icmp --  *      *       0.0.0.0/0            0.0.0.0/0
7       74  5440 ACCEPT     all  --  lo     *       0.0.0.0/0            0.0.0.0/0
8       16   864 ACCEPT     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           state NEW tcp dpt:22
9     170K   39M REJECT     all  --  *      *       0.0.0.0/0            0.0.0.0/0           reject-with icmp-host-prohibited

2. Inject rule, as long as it's before the REJECT line
# iptables -I INPUT 5 -p tcp -m state --state NEW -m tcp --dport 80 -j ACCEPT

3. Save
# service iptables save

4. Add httpd_t to the list of permissive domains (So we don't need to turn off selinux)
# yum install policycoreutils-python
# semanage permissive -a httpd_t

Perl specific installs for Centos 6.6

1. Enable RPMForge Repository

# wget http://packages.sw.be/rpmforge-release/rpmforge-release-0.5.3-1.el6.rf.x86_64.rpm
# rpm -Uvh rpmforge-release-0.5.3-1.el6.rf.x86_64.rpm
# rpm --import http://dag.wieers.com/rpm/packages/RPM-GPG-KEY.dag.txt

2. Install perl installs

MANUAL:
1. Dependency of Net::SSH::Perl
# wget http://download.opensuse.org/repositories/home:/csbuild:/Perl/CentOS_CentOS-6/x86_64/perl-Math-GMP-2.04-2.5.x86_64.rpm
# rpm -Uvh perl-Math-GMP-2.04-2.5.x86_64.rpm

2. Dependency of gnuplot for Chart::Graph::Gnuplot
# wget http://www.my-guides.net/en/images/stories/fedora12/msttcore-fonts-2.0-3.noarch.rpm
# rpm -Uvh msttcore-fonts-2.0-3.noarch.rpm

YUM:
# yum install perl-Math-BigInt-GMP
# yum install perl-Math-Pari
# yum install perl-Archive-Zip
# yum install perl-Chart
# yum install perl-DBI
# yum install perl-DBD-MySQL
# yum install perl-Data-Compare
# yum install perl-Date-Manip
# yum install perl-JSON
# yum install perl-Net-Telnet
# yum install perl-NetAddr-IP
# yum install perl-Statistics-Descriptive
# yum install perl-Text-Table
# yum install perl-XML-Simple
# yum install perl-XML-Writer
# yum install gnuplot

CPAN:
# cpan Data::Diff
# cpan HTML::TextToHTML
# cpan XML::SemanticDiff
# cpan Chart::Graph - this didn't install

Force installed:
cpan[1]> force install Net::Telnet::Brcd

Install different versions of Perl on Linux using Perlbrew

Got from here and here. What is perlbrew.

1. Install perfbrew
$ curl -kL http://install.perlbrew.pl | bash

2. Modify .bashrc and add:
source ~/perl5/perlbrew/etc/bashrc

3. Initialize
$ perlbrew init

4. Select mirror
$ perlbrew mirror

5. See what's available
$ perlbrew available
  perl-5.20.1
  perl-5.18.4
  perl-5.16.3
  perl-5.14.4

6. Install perls
$ perlbrew install perl-5.20.1  # did not work for Centos 6.5
$ perlbrew --notest install perl-5.20.1

7. See what were installed
$ perlbrew list

8. Swith to an installation and set it as default
$ perlbrew switch perl-5.20.1

9. Temporarily use another version only in current shell.
$ perlbrew use perl-5.20.1
$ perl -v

10. Or turn it off completely. Useful when you messed up too deep. Or want to go back to the system Perl.
$ perlbrew off

11. Use 'switch' command to turn it back on.
$ perlbrew switch perl-5.20.1

12. Exec something with all perlbrew-ed perls
$ perlbrew exec -- perl -E 'say $]'

13. Install cpanm
$ perlbrew install-cpanm

14. Install cpan modules
$ cpanm install File::Copy::Recursive XML::Simple etc

Ruby Notes

While reading RubyMonk tutorials

1. Truthiness of objects in Ruby
Only objects false and nil equates to false. Every other object like say 1, 0, "" are all evaluated to be true.

2. Use break in infinite loops

loop do
  monk.meditate
  break if monk.nirvana?
end

3. Append to an array, use << operator

[1, 2, 3, 4, 5] << 'woot'
[1, 2, 3, 4, 5, "woot"]

4. Filter elements of an array, use 'select'

names = ['rock', 'paper', 'scissors', 'lizard', 'spock']
names.select { |word| word.length > 5 }

5. Delete elements of an array, use 'delete_if'

[1,2,3,4,5,6,7,8,9].delete_if { |i| i % 2 == 0 }

6. Methods are themselves objects, and responds using 'call'

next_method_object = 1.method("next")
puts next_method_object.call

7. Beware of shallow object copies, to do a deep copy use Marshal

new_job = Marshal.load(Marshal.dump(job))

8. Use heredoc for convenient multiline strings. The dash ignores spaces before placeholder. The gsub takes care of removing spaces at beginning of each line.

def long_message
  puts <<-EOT.gsub(/^\s*/, '')
    Here goes a very long message...
    Sincerely,
    Dr. Foobear
  EOT
end

7. Use 'send' when testing private methods

# obj.send(:method_name, args)
@parser.send(:running?, test_strings)