How to install the Perl module Data::Dumper on Linux - RHEL, CentOS or Amazon AMI?

Below is an error message that could get thrown while installing any Bitnami package (say Bitnami Mediawiki package) on a Linux

Error: Error running /opt/app_name/mysql/scripts/myscript.sh 

/opt/app_name/mysql ****: FATAL ERROR: please install the following 

Perl modules before executing scripts/mysql_install_db:

Data::Dumper

The error states that you have install the Perl Module Data::Dumper. Run the below command :

yum install "perl(Data::Dumper)"

Follow through the rest of the instructions on the command line to complete the installation. 

How to hide or remove the View History tab on Mediawiki

Below are the steps to remove/disable/hide the View History tab on Mediawiki. This works as of early 2016 on Mediawiki 1.26x. Hope it helps!

1. Login to your apps/mediawiki/htdocs directory. This is the directory which contains the LocalSettings.php file.
2. Edit the LocalSettings.php file (open in text editor).  Add (append) the following lines

#====Begin : code to hide/remove View Source tab from Mediawiki====
function efAddSkinStyles(OutputPage &$out, Skin &$skin) {

    if(!$skin->getUser()->isLoggedIn()) {

        if ($skin->getSkinName() == 'vector') {

            $out->addInlineStyle('#ca-history { display:none; }');

        }

    } else {

        if ($skin->getSkinName() == 'vector') {

            $out->addInlineStyle('#ca-view { display:none; }');

        }

    }

    return true;

}

$wgHooks['BeforePageDisplay'][] = 'efAddSkinStyles'; 
#====End of code====

Setup WordPress On Amazon EC2 : Installation steps with Linux commands cheat sheet

This is a real quick guide to setup WordPress On Amazon EC2. It is a direct result of following a Youtube tutorial on the same subject by a guy named Avishai Sam Bitton, who is the Marketing Director at Imonomy & Founder of Go Social.

The Youtube tutorial by itself was great. In 10 minutes, Avishai shows you how to go from creating a Linux instance to the WordPress admin page. It is done on the Amazon Linux AMI (not Ubuntu or RHEL). The only missing thing is the Linux commands cheat sheet (copy-paste-able) which I will cover in the following paragraphs. I will try to provide maximum information in minimal words.

Here is the actual video and what follows is my notes on the same :

To setup a WordPress blog on the Amazon EC2 infrastructure, you need to know and do the following as a prerequisite:

• Have Putty and PuttyGen installed (or ready for use)
• Have basic understanding of Linux concepts and commands. Know how to use putty, and optionally understand security concepts.
• You should have created an Amazon AWS account. A credit card signup is required even though the basic Linux instance (micro instance) is free for 12-months.

Once you're ok with the above, follow these steps.

Part A

1. Login to the Amazon AWS console.
2. Select :  EC2  - Virtual servers in the cloud.
3. Under Create Instance, click on Launch Instance.
4. Select Amazon AMI Linux - 64 bit
5. Check settings. Maintain defaults. Keep clicking next - until you reach the Configure Security Group section.
6. Click Add Rule twice : 
• One for the HTTP (port 80) 
• another for the HTTPS (port 443). 
• Also add a third one and select Custom TCP port. Enter port 8080 (if your apache or nginx server runs on this port)
• The SSH rule is already added with port 22.
7. Click Review and Launch. Click Launch. This opens a dialog to create a new key pair. 
8. Create a new key pair. Download the pem file to your local folder.
9. Now click Launch Instance (wait for 5 mins for startup)
10. In the meantime, convert the pem file to ppk file. 
• Windows :  PuttyGen tool, go to Menu->Convert->Import->Save file with ppk extension to your local drive.
• If you are on Mac, no need to convert. You can use the pem file to login directly using the generated Elastic IP address (steps given below).

Part B

1. The instance which you launched couple of steps back should now be running(green tick mark)
2. On the Left pane -> click Elastic IPs -> Allocate New Address -> Yes,Allocate
3. Right click on the allocated Elastic IP -> Associate Address -> running instance (some 10-character code). Click Associate.
4. Go to EC2 Dashboard -> Running Instances. Check the Public IP and Elastic IP (both should be same).
5. Copy the IP address. Open Putty and copy the IP address (say 11.22.33.44) into putty's Host.
6. Go to SSH->Auth, browse open the converted ppk file. Go back to Session and click Open. Putty's black screen should open up.
• Windows  : Login as : ec2-user
• Mac : 
  ssh -i keyfile.pem ec2-user@11.22.33.44

Part C - The Linux Commands (aka Cheat Sheet)

Once you've logged in as the ec2-user, type in the below commands one after another.
Note: In all the "install" commands, press "y" if the shell asks for install confirmation.

Commands	Notes
sudo yum update	Updates all software patches on the instance.
sudo su	Switching to root user
yum install httpd	Installs Apache server
service httpd start	Starts Apache server
yum install php php-mysql	Installs PHP
yum install mysql-server	Installs MySQL
service mysqld start	Starts MySQL server
mysqladmin -uroot create myblog	myblog will the name of the database in this example)
mysql_secure_installation	Follow these steps: * Enter current password for root: just press enter key * Set root password? : Y (enter password twice) * Remove Anonymous Users? : Y * Disallow root login remotely: Y * Remove test database and access to it? : Y * Reload privileges table now? : Y
cd /var/www/html	Go to this directory
wget http://wordpress.org/latest.tar.gz	Download the latest version of Wordpress
tar -xzvf latest.tar.gz	Extract Wordpress
mv wordpress myblog	Rename the the blog to myblog
cd myblog	Go to the myblog directory
mv wp-config-sample.php wp-config.php	Rename the php config file.
vi wp-config.php	Edit the wp-config.php file with the given information : * define('DB_NAME', 'myblog') * define('DB_USER', 'root') * define('DB_PASSWORD', 'yourpassword') * press escape key * :wq! (to save and exit)
service httpd restart	Restarts Apache server

Now, open your browser, and enter : http://IPAddress/myblog  (in our case, http://11.22.33.44/myblog).
Your Wordpress blog's Admin installation page should be ready for configuration.
If your web server is running on port 8080, then use the url : http://11.22.33.44:8080/myblog.

How to find lines not containing (matching) a string in Notepad++

 In Notepad++, you might have a requirement to find or replace lines which do NOT match a particular string.
Lets say you have the following lines in your text file - and you would like to the find lines NOT containing the string "USA"

Apple - USA
Airbus - France
Google -USA
IBM - USA
SAP - Germany
TESCO - UK

For this, you will have to use the Notepad++ Regex find option

Here's how:

• Press Ctrl + F to pop open the Find dialog box
• Select the Regular Expression radio button
• Type in the find box : ^(?!.*USA).*$ 
• Now find or replace.

Here are couple of awesome books to understand more about Regular expressions :

• Mastering Regular Expressions - by Jeffrey Friedl ( Amazon.com | Amazon.in ) 
• Regular Expressions Cookbook by Jan Goyvaerts, Steve Levithan ( Amazon.com | Amazon.in)

Here's a screenshot of my notepad++ screen.

 

How to install Beautiful Soup or BS4 on Windows?

BeautifulSoup is a Python module which is meant for web scraping. That is, using Python, you can fetch an html webpage (using a module such as urllib2), and then obtain meaningful information out of the html file (using the BeautifulSoup module).

Here are the steps to download and install BeautifulSoup on Windows. It assumes you have already installed python and you know how to use an archiving tool such as 7-zip.

1) Download the BeautifulSoup compressed file from the below link:
http://www.crummy.com/software/BeautifulSoup/bs4/download/

In my setup, I have downloaded a file named beautifulsoup4-4.2.1.tar.gz.

2) Extract the archive using a tool such as 7-zip. Once you have extracted the files, open cmd prompt, and go to directory named beautifulsoup4-4.2.1

3) Run the following command to install BeautifulSoup
C:\>python setup.py install

4) Test the installation with this command :
>>>from bs4 import BeautifulSoup

If you see the python prompt (>>>) in the next line without any errors, then it means BS4 is successfully installed.

For detailed coverage, check out this book : Getting Started with Beautiful Soup

Oracle SQL Query to print Unix Timestamp

The actual query is available in http://jehiah.cz/a/oracle-date-to-unix-timestamp , but here is a slightly modified version which strips the decimal points and prints only the elapsed seconds.
---
SELECT abs(to_number(((sysdate - to_date('01-JAN-1970','DD-MON-YYYY')) * (86400)))) as dt FROM dual;
---

Ubuntu Linux - Change from GUI mode to Command line / Text mode

Simple stuff - just documenting my learnings

So here's how we change Ubuntu from its usual GUI mode to the Command line mode (black screen / text mode)

Note : If"sudo" is used before a command, then you will have to enter root password.

• Open the Terminal, and cd /etc/default
• Open the "grub" file in vi editor as root : sudo vi grub
• Change the property GRUB_CMDLINE_LINUX_DEFAULT from "quiet splash" to "text". See below
• ========
• #GRUB_CMDLINE_LINUX_DEFAULT = "quiet splash"
• GRUB_CMDLINE_LINUX_DEFAULT = "text"
• ========
• Run this command to update grub : sudo update-grub
• Reboot Ubuntu : sudo /sbin/reboot

On reboot, you should be able to see the command-line screen instead of GUI.