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RoR or Ruby on Rails is an open source, cross-platform web development framework that provides a structure to the developers for their code. It helps them create applications and websites by abstracting and simplifying the repetitive tasks faced during development. It is called Ruby on Rails because Rails is written in the Ruby programming language, exactly how Symfony and Zend are written in PHP and Django in Python. Rails provide default structures for databases, web servers, and web pages. Famous applications like Soundcloud, Github and Airbnb are all based on Rails.

Ruby on Rails is licensed under MIT and was first released in December 2005. All of its repositories are available on Github, including the latest release to date.

This tutorial explains a step-by-step process for installing and configuring Ruby on Rails with all its prerequisites. Later, we will explain how to install and configure the PostgreSQL Database in order to create your first Rails project.The article also explains how to create a simple CRUD interface, making your application more interactive and useful.

We have run the commands and procedures mentioned in this article on a Ubuntu 18.04 LTS system. We are using the Ubuntu command line, the Terminal, in order to install and configure Ruby on Rails. You can access the Terminal application either through the system Dash or the Ctrl+Alt+T shortcut.

Ruby on Rails Installation

In order to install Ruby on Rails, you first need to have the latest versions of some prerequisites installed and configured on your system, such as:

• RVM-Ruby Version Manager
• Ruby
• Nodejs-Javascript runtime
• Ruby Gems-Ruby Package Manager

In this section, we will first have our system ready by first installing all these step-by-step, setting up their latest versions, and then finally install Ruby on Rails.

1. Install Ruby Version Manager (RVM)

The Ruby Version Manager helps us in managing Ruby installation and configuring multiple versions of Ruby on a single system. Follow these steps in order to install the RVM package through the installer script:

Step1: Add the RVM key to your system

Run the following command in order to add the RVM key; this key will be used when you install a stable version of RVM:

$ gpg –keyserver hkp://keys.gnupg.net –recv-keys 409B6B1796C275462A1703113804BB82D39DC0E3
7D2BAF1CF37B13E2069D6956105BD0E739499BDB

Step2: Install Curl

We will be installing RVM through Curl. Since it does not come by default with the latest versions of Ubuntu, we will need to install it through the following commands as sudo:

$ sudo apt install curl

Please note that only authorized users can add/remove and configure software on Ubuntu.

The system will prompt you with a Y/n option in order to confirm the installation. Please enter Y to continue, after which, Curl will be installed on your system.

Step3: Install the RVM Stable version

Now run the following command in order to install the latest stable version of RVM.

$ curl -sSL https://get.rvm.io | bash -s stable –ruby

This command will also automatically install all the required packages needed to install RVM.

The process will take some time depending on your Internet speed, after which RVM will be installed on your system.

Step4: Setup RVM source folder

Please note that the last few lines of the RVM installation output suggest running the following command:

$ source /usr/local/rvm/scripts/rvm

This is used to set the source folder to the one mentioned in the output. You need to run this command in order to start using RVM.

You might get the following output when setting up the source:

In that case, run the following commands on your system:

$ source ~/.rvm/scripts/rvm
$ echo “source ~/.rvm/scripts/rvm” >> ~/.bashrc
$ source ~/.bashrc

Now the source for RVM is set. You can check the version number of RVM installed on your system through the following command:

$ rvm –version

This output also ensures that RVM is indeed installed on your system.

2. Configure Latest Version of Ruby as System Default

When you install RVM, the latest version of Ruby is also installed on your system. What you need to do, however, is to set up your system to use the latest version of Ruby as the system default. Follow these steps to do so:

Step1: Setup RVM latest stable version

First, we need to update the RVM on our system with the latest stable version available on https://get.rvm.io

Run the following command to do so:

$ rvm get stable –autolibs=enable

Step2: Get the list of all available Ruby versions

The following command gives you the list of all Ruby versions released till date:

$ rvm list known

Through this list, please choose the latest version of Ruby available. As you can see in the output, Ruby 2.6.0 is the latest version available.

Step3: Install the latest Ruby version

Now install the latest version of Ruby that you have selected in the previous step, by running the following rvm command:

$ rvm install ruby-2.6

The process may take some time depending on your Internet speed, after which the selected number of Ruby will be installed on your system.

Step4: Set the latest version of Ruby as default

The following rvm command will help you in setting the latest installed version of Ruby as the system default:

$ rvm –default use ruby-2.6

You can see that now my system will be using Ruby 2.6.0-rc1 as the default Ruby version.

This can also be verified by running the following version command:

$ ruby -v

3. Install Nodejs and the gcc compiler

Before starting with the Rails development on Linux, we recommend using Nodejs as the Javascript runtime. It is a prerequisite for compiling Ruby on Rails asset pipeline.

Step1: Install the latest version of Nodejs

Use the following command in order to install the Nodesource repository to your system:

$ curl -sL https://deb.nodesource.com/setup_10.x | sudo -E bash –

Now install the latest version of Nodejs through the following apt command as sudo:

$ sudo apt install -y nodejs

The latest available version of Nodejs 10 will be installed on your system

Step2: Install the gcc compiler

The gcc compiler is another prerequisite that you need to install before performing any Rails development. Use the following command as sudo in order to install it:

$ sudo apt install gcc g++ make

4. Configure Latest Version of RubyGems as System Default

When you install RVM, RubyGems is also installed on your system. What we need to do, however, is to set up our system to use the latest version of RubyGems the system default. Ruby Gems is basically the Ruby on Rails package manager that comes with the command line tool-gem.

Run the following gem command in order to update the system to use the latest version:

$ gem update –system

Now when you check the version number through the following command, you will see that your system is using the latest version of RubyGems in the command line:

$ gem -v

5. Install Ruby on Rails

Finally, after installing all the prerequisites, we can now install Ruby on Rails on our system by following these steps:

Step1: Look up for the latest available version

The RubyGems website maintains all the versions of Ruby on Rails till date, on the following link:

https://rubygems.org/gems/rails/versions

Choose the latest version of Ruby on Rails that you would like to install. At the time of writing this article, the latest available version is 5.2.2

Step2: Install the latest Ruby on Rails version

You can install the latest version of Ruby on Rails through the gem command line tool as follows:

$ gem install rails -v 5.2.2

The installation process might take some time depending on your Internet connection.

After the installation is complete, run the following command to view the Rails version installed on your system.

$ rails -v

The command also verifies that Ruby on Rails is indeed installed on your system.

Rails Development

Ruby on Rails supports many databases such as SQLite, MySQL, and PostgreSQL. In this section, we will explain how to start with the Rails development with the PostgreSQL database. This will include:

• Installing PostgreSQL Database
• Configuring PostgreSQL and Creating Roles
• Your First Rails application
• Creating a simple CRUD with PostgreSQL database on Rails

1. Install and Setup PostgreSQL Database

Step1: Install PostgreSQL

Use the following apt command as sudo in order to install the PostgreSQL database and some other required packages:

$ sudo apt install postgresql postgresql-contrib libpq-dev -y

Step2: Start and enable the PostgreSQL service

Once PostgreSQL is installed, you need to start the ‘postgresql’ service through the following command:

$ systemctl start postgresql

The system will prompt you with an authentication dialog, as only an authorized user can enable services on Ubuntu. Enter the admin password and click the Authenticate button after which the service will start.

The next step is to enable the service through the following command:

$ systemctl enable postgresql

The system will prompt you with a similar authentication dialog multiple times; enter the admin password each time and click the Authenticate button after which the service will be enabled.

Step3: Verify installation

$ Please run the following command in order to view a details stats report of your PostgreSQL installation:

$ dpkg –status postgresql

2. Configure PostgreSQL and Create Roles

PostgreSQL applications can be created by user or roles. By default, a “postgres” user exists which is a superuser and it can create and migrate databases and also manage other user roles.

Initially, you can log in as sudo on PostgreSQL through the following command:

$ sudo -u postgres psql

Here you can change the password of postgres as follows:

postgress=# password postgres

Create a Role

A superuser can create a new user role through the following command:

$ create role “role_name” with createdb login password “‘password’”’ ;

Example:

postgress=# create role dev_rails with createdb login password ‘rockon123’ ;

We are creating a role by the name of “dev_rails”. This is a user that will create a db for our first Rails application.

A superuser can view the list of roles existing on PostgreSQL as follows:

postgress=# du

Use Ctrl+z to exit PostgreSQL.

3. Your First Rails application

Now we will create our first Rails application with PostgreSQL as the default database. This involves the following steps:

Step1: Create a new Rails application

Create a new project by the name of “firstapp”, or any other name, through the following command and specify PostgreSQL as the database:

$ rails new firstapp -d postgresql

This will create a project folder in your home folder as follows:

$ ls

Step2: Configure your Rails project to incorporate the PostgreSQL user role

Now we want the user role we created in PostgreSQL to be able to create a database in the Rails application. For this, you need to edit the database.yml file located in your newly created application’s folder in the /config/ folder.

Move to your first application and then the config folder as follows:

$ cd /firstapp/config

Here you will see the database.yml file. You can edit this file through your favorite text editor. We will be doing so through the Nano editor by using the following command:

$ nano database.yml

In this file, you will be able to see mainly three sections:

• Development
• Test
• Production

We will need to configure the Development and Test sections of the file.

Make the following configurations in the Development section

database: firstapp_development username: dev_rails password: rockon123 host: localhost port: 5432

And, the following in the Test section:

database: firstapp_test username: dev_rails password: rockon123 host: localhost port: 5432

Note: Please make sure that the syntax is correct. Each line should be preceded by 2 spaces and NOT tabs.

Save the file by pressing Ctrl+X, then Y and then by hitting Enter.

Step3: Generate and then migrate the Database

Generate the database through the following rails command:

$ rails db:setup

Please make sure that there are no errors. Most errors are due to the wrong syntax in the database.yml file or the inconsistency in the username and password from the one you created in PostgreSQL.

After the successful generation, migrate the database through the following rails command:

$ rails db:migrate

Step4: Start the Puma Rails web server

After completing the application setup, please enter the following command in order to start the default Puma web server:

$ rails s -b localhost -p 8080

Or in our case,

$ rails s -b 127.0.0.1 -p 8080

After this command, your first Rails application is running on the local host at port 8080.

Step5: Open the default Rails Project Homepage

You can view your database successfully being hosted on the default Rails Project homepage by entering this URL in one of your web browsers:

http://localhost:8080/

You can also use your localhost IP, like us, in the above-mentioned URL:

You can not perform any CRUD operation on this simple application. Follow the article some more in order to make your application a little more interactive.

4. Create a simple CRUD with PostgreSQL database on Rails

Let us make our application more interactive by implementing a CRUD(Create, Read, Update, Delete) interface.

Step1: Create a Scaffold in Rails

Run the following command in order to create a scaffold in your Rails application folder

$ rails g scaffold Post title:string body:text

Then migrate the database by running the following command:

$ rake db:migrate

Step2: Run the application on Puma Rails Web Server

Next, run your application on the localhost by running the Puma web server again through the following command:

$ rails s -b localhost -p 8080

You can also use your localhost IP, like us, for the above-mentioned command:

$ rails s -b 127.0.0.1 -p 8080

Step3: Open the ‘Posts’ page in Rails Project

You can view your database successfully being hosted on the Rails Project page by entering the URL in one of your web browsers:

http://localhost:8080/posts/

Or use a localhost IP like us:

http://127.0.0.1:8080/posts

You will be able to see a simple CRUD interface through which you can create, edit, show and destroy posts.

When I created a post using the New Post link, here is how my posts page looked like:

You have now successfully completed the entire process of installing Ruby on Rails on your Ubuntu and then creating a sample application using the PostgreSQL database. This will serve as a basis for you to develop more productive and interactive database applications through Ruby on Rails.

Source

Your Linux machine is only as good as you make it. To make it into a powerful machine, you need to install the right packages, use the right configurations among a host of other things. Talking about packages; in this article I would be taking a primer on the APT package management tool. Similar to YUM for RHEL(RedHat Enterprise Linux) based Linux distributions—which was discussed here—APT(Advanced Packaging Tool) is for managing packages on Debian and Ubuntu based Linux distributions.This article isn’t planned to discuss all the powers of the APT package management tool, instead it is intended to give you a quick look into this tool and how you can use it. It would serve well for reference purposes and understanding how the tool works. Without much ado, let’s get started.

Location

Just like many Linux tools, apt is stored in the /etc directory—contains the configuration files for all the programs that run on Linux systems—and can be viewed by navigating to the directory.

Apt also has a configuration file which can be found in the /etc/apt directory with the file name apt.conf.

You would be doing a lot of package installations with apt, therefore it would go a long way to know that package sources are stored in a sources.list file. Basically, apt checks this file for packages and attempt to install from the list of packages—let’s call it a repository index.

The sources.list file is stored in the /etc/apt directory and there is a similar file, named sources.list.d. It isn’t actually a file, but a directory which keeps other sources.list files. The sources.list.d directory is used by Linux for keeping some sources.list files in a separate place—outside the standard /etc/apt directory.

The confusion: APT vs APT-GET

Yes, a lot of people actually mistake apt to be the same as apt-get. Here’s a shocker: they are not the same.

In truth, apt and apt-get work similarly however the tools are different. Let’s consider apt to be an upgrade on apt-get.

Apt-get has been in existence before apt. However apt-get doesn’t exist in isolation as it works together with other apt packages such as apt-cache and apt-config. These tools when combined are used to manage linux packages and have different commands as well. Also these tools are not the easiest to use as they work at a low level, which an average Linux user couldn’t care less about.

For this reason, apt was introduced. The version 1.0.1 of APT has the following on the man page, “The apt command is meant to be pleasant for end users and does not need to be backward compatible like apt-get.”

Apt works in isolation and doesn’t need to be combined with other tools for proper Linux administration, plus it is easy to use.

For an average Linux user, the commands are all that matter. Through the commands, tasks are executed and actual work can be done. Let’s take a look at the major apt commands.

Get Help

The most important of all the commands to be discussed in this article is the command used to get help. It makes the tool easy to use and ensures you do not have to memorize the commands.

The help provides enough information to carry out simple tasks and can be accessed with the command below:

You would get a list of various command combinations from the result, you should get something similar to the image below:

If you desire, you could check out the apt man pages for more information. Here’s the command to access the man pages:

Search for package

For a lot of operations, you would need to know the exact name of a package. This and many more uses are reasons to make use of the search command.

This command checks all the packages in the repository index, searches the keyword in the package descriptions and provides a list of all packages with the keyword.

Check package dependencies

Linux packages have dependencies, these dependencies ensure they function properly as the packages break when the dependencies break.

To view a package’s dependencies, you use the depends command.

apt depends <package name>

Display package information

Displaying a package’s dependencies is one information you would find useful. However, there are other package details you can get. For me, it would be less productive to memorize all the commands to access other details such as the package’s version, download size etc.

You can get all of a package’s information in one attempt using the apt command as seen below:

Install package

One of Linux’s strongest points is the availability of lots of powerful packages. You can install packages in two ways: either through the package name or through a deb file—deb files are debian software package files.

To install packages using the package name, the command below is used:

apt install <package name>

As stated earlier, you need to know the package name before using it. For example, to install Nginx the command would be apt install nginx.

The other means of installing packages is the through the deb file if available. When installing a package through its deb file, apt fetches the package dependencies itself and downloads it so you do not have to worry about them.

You can install deb files using the absolute path to the files with the command below:

apt install </path/to/file/file_name.deb>

Download package

If for some reason, you need to download a package without having it installed, you can do so using the download command.

This would download the package’s deb file into the directory where the command was run. You can download packages using the command below:

apt download <package name>

If you are then interested in installing the .deb file, you can then install using the install command.

Update repository index

Remember we talked about sources.list earlier? Well, when a new version of a package is released, your linux machine is not able to install it yet because it would not indicate. To have it indicate, it needs to reflect in the sources.list file and this can be done using the update command.

This command refreshes the repository index and keeps it up-to-date with the latest changes to the listed packages.

Remove packages

Packages break. Packages become obsolete. Packages need to be removed.

Apt makes it easy to remove packages. Here are different conditions to removing packages: removing the binary files and keeping the config files, removing the binary files and the config files.

To remove the binary files alone, the remove command is used.

apt remove <package name>

More than one package can be removed, so you can have apt remove nginx top to remove the Nginx and top packages at the same time.

To remove the configuration files, the purge command is used.

If you wish to do both at once, the commands can be combined as seen below:

apt remove –purge <package name>

Before proceeding, it should be known that when packages are removed, their dependencies remain i.e. they are not removed too. To remove the dependencies while uninstalling, the autoremove command is used as seen below:

apt autoremove <package name>

List packages

Yes, you can have the packages on your Linux machine listed. You can have a list of all packages in the repository index, installed packages and upgradeable packages.

Regardless what you intend doing, the list command would be used.

The command above is used to list all the packages available in the repository index.

The command above is used to list the packages installed on your Linux machine.

The command above is used to list the packages installed on your machine that have upgrades available.

Updating packages

When it comes to packages, it’s not all about installing and removing packages; they need to be updated too.

You can decide to upgrade a single package or all packages at once. To update a single package, the install command is going to be used. Surprising right? Yes, however we are going to be adding the –only-upgrade parameter.

apt install –only-upgrade <package name>

This works when you intend upgrading just one package. However, if you want to upgrade all the packages you would need to use the upgrade command.

The following command would be used to make such an upgrade:

It should be noted that the upgrade command doesn’t remove dependencies and even if the upgraded packages do not need them anymore i.e. they are obsolete.

System upgrade

Unlike the regular upgrade, the full-upgrade command to be discussed here performs a complete system upgrade.

With the full-upgrade command, obsolete packages and dependencies are removed and all packages (including system packages) are upgraded to their latest versions.

The command for doing this, is full-upgrade as seen below:

Conclusion

Apt is a powerful tool that makes the use of Debian and Ubuntu based Linux distributions a wonderful experience. Most of the apt commands listed here require root permissions, so you may need to add sudo to the start of the commands.

These commands are just a tip of the iceberg of the immense powers that the apt tool possesses, and they are powerful enough to get you comfortable with managing packages on your Linux machine.

Source

When in Rome: finishing the Roman numeral converter script.

In my last article, I started digging in to a classic computer science puzzle: converting Roman numerals to
Arabic numerals. First off, it more accurately should be called Hindu-Arabic, and it’s worth
mentioning that it’s believed to have been invented somewhere between the first and fourth
century—a counting system based on 0..9 values.

The script I ended up with last time offered the basics of parsing a specified Roman numeral and
converted each value into its decimal equivalent with this simple function:

mapit() {
case $1 in
I|i) value=1 ;;
V|v) value=5 ;;
X|x) value=10 ;;
L|l) value=50 ;;
C|c) value=100 ;;
D|d) value=500 ;;
M|m) value=1000 ;;
* ) echo “Error: Value $1 unknown” >&2 ; exit 2 ;;
esac
}

Then I demonstrated a slick way to use the underutilized seq command to parse a string character by
character, but the sad news is that you won’t be able to use it for the final Roman numeral to
Arabic numeral converter. Why? Because depending on the situation, the script sometimes
will need to jump two ahead, and not just go left to right linearly, one character at a time.

Instead, you can build the main loop as a while loop:

while [ $index -lt $length ] ; do

our code

index=$(( $index + 1 ))
done

There are two basic cases to think about in terms of solving this algorithmic puzzle: the subsequent
value is greater than the current value, or it isn’t—for example, IX versus II. The first is 9
(literally 1 subtracted from 10), and the second is 2. That’s no surprise; you’ll need to know both the
current and next values within the script.

Sharp readers already will recognize that the last character in a sequence is a special case,
because there won’t be a next value available. I’m going to ignore the special case to start with,
and I’ll address it later in the code development. Stay tuned, sharpies!

Because Bash shell scripts don’t have elegant in-line functions, the code to get the current and
next values won’t be value=mapit(romanchar), but it’ll be a smidge clumsy with its use of the global
variable value:

mapit $
currentval=$value

mapit $
nextval=$value

It’s key to realize that in the situation where the next value isn’t greater than the current value
(for example, MC), you can’t automatically conclude that the next value isn’t going to be part of a
complex two-value sequence anyway. Like this: MCM. You can’t just say M=1000 and C=500, so let’s
just convert it to 1500 and process the second M when we get to it. MCM=1900, not 2500!

The basic logic turns out to be pretty straightforward:

if [ $nextval -gt $currentval ] ; then
sum=$(( $sum + $nextval – $currentval ))
else
sum=$(( $sum + currentval ))
fi

Done!

Or, um, not. The problem with the conditional code above is that in the situation where you’ve
referenced both the current and next value, you need to ensure that the next value isn’t again
processed the next time through the loop.

In other words, when the sequence “CM” is converted, the M shouldn’t be converted yet
again the second time through the loop.

This is precisely why I stepped away from the for loop, so you can have some passes through the loop
be a +1 iteration but others be a +2 iteration as appropriate.

With that in mind, let’s add the necessary line to the conditional statement:

if [ $nextval -gt $currentval ] ; then
sum=$(( $sum + $nextval – $currentval ))
index=$(( $index + 1 ))
else
sum=$(( $sum + currentval ))
fi

Remember that the very bottom of the while loop still has the index value increment +1. The above
addition to the conditional statement is basically that when the situation of next > current is
encountered, the script will process both values and jump ahead an extra character.

This means that for any given Roman numeral, the number of times through the loop will be equal to or
less than the total number of characters in the sequence.

Which means the problem is now solved except for the very last value in the sequence. What happens if
it isn’t part of a next-current pair? At its most simple, how do you parse “X”?

That turns out to require a bunch of code to sidestep both the conversion of nextval from the string
(which will fail as it’s reaching beyond the length of the string) and any test reference to
nextval.

That suggests a simple solution: wrap the entire if-then-else code block in a conditional that tests
for the last character:

if [ $index -lt $length ] ; then
if-then-else code block
else
sum=$(( $sum + $currentval ))
fi

That’s it. By George, I think you’ve got it! Here’s the full while statement, so you can
see how this fits into the overall program logic:

while [ $index -le $length ] ; do

mapit $
currentval=$value

if [ $index -lt $length ] ; then
mapit $
nextval=$value

if [ $nextval -gt $currentval ] ; then
sum=$(( $sum + $nextval – $currentval ))
index=$(( $index + 1 ))
else
sum=$(( $sum + $currentval ))
fi
else
sum=$(( $sum + $currentval ))
fi

index=$(( $index + 1 ))

done

It turns out not to be particularly complex after all. The key is to recognize that you need to parse the
Roman number in a rather clumped manner, not letter by letter.

Let’s give this script a few quick tests:

$ sh roman.sh DXXV
Roman number DXXV converts to Arabic value 525
$ sh roman.sh CMXCIX
Roman number CMXCIX converts to Arabic value 999
$ sh roman.sh MCMLXXII
Roman number MCMLXXII converts to Arabic value 1972

Mission accomplished.

In my next article, I plan to look at the obverse of this coding challenge, converting Arabic numerals to
Roman numeral sequences. In other words, you enter 99, and it returns XCIX. Why not take a stab at
coding it yourself while you’re waiting?

Source

Parted is a command line tool for managing disk partitions on Linux. Parted can be used to work with both MSDOS and GPT partition tables. Parted can be used to do many low level partitioning tasks easily. In order to use parted correctly, you will need a lot of knowledge on the physical structure of the disk such as the block size of the disk. In this article, I will show you how to use parted on Linux. I will be using Ubuntu 18.04 LTS for the demonstration. So, let’s get started.

If you’re using Ubuntu or any Debian based Linux distributions, then you can easily install parted as it is available in the official package repository. First, update the APT package repository cache with the following command:

The APT package repository cache is updated.

Now, run the following command to install parted:

$ sudo apt install parted

Now, press y and then press <Enter> to continue.

Parted should be installed.

On CentOS/RHEL 7, you can install parted with the following command:

$ sudo yum install parted -y

Finding Storage Device Identifiers:

Before you can start working with parted, you have to know which storage device you need to partition.

You can run the following command to list all the attached storage devices on your computer:

$ sudo lshw -class disk -short

As you can see, I have 2 storage devices on my computer, /dev/sda and /dev/sdb. Here, /dev/sdb is my 32GB USB thumb drive. This is the one I want to partition.

Opening Storage Device with parted:

Now that you know which storage device you want to partition, you can open parted as follows:

NOTE: Make sure you change /dev/sdb to the storage device that you want to partition.

Parted should be opened. Now, you can run many of the parted commands to partition your desired storage device any way you want.

Switching to Different Storage Device:

You can also start parted without specifying which storage device to open beforehand as follows:

As you can see, parted is started. By default, /dev/sda, the first/primary storage device is selected.

You can list all the storage devices on your computer with the following parted command:

As you can see, the storage devices on my computer /dev/sda and /dev/sdb are listed along with their physical size.

Now, you can use the select parted command to select the storage device (let’s say /dev/sdb) that you want to partition as follows:

As you can see, /dev/sdb is selected.

Creating a New Partition Table:

You can create GPT and MSDOS partition table with parted.

To create a GPT partition table, run the following parted command:

To create a MSDOS partition table, run the following parted command:

I will go for MSDOS partition table as I am partitioning a USB thumb drive. The procedure for the GPT partition creation is the same.

Now, type in Ignore and press <Enter>.

When you create a new partition table, all the existing partitions will be erased. If you’re okay with it, type in Yes and then press <Enter>.

For some reason, the changes can’t be applied immediately. But it’s alright. Type in Ignore and press <Enter>.

A new partition table should be created.

Creating New Partitions:

You can create a new partition with the following parted command:

Now, type in either primary or extended depending on whether you want to create a primary or extended partition. Once you’re done, press <Enter>.

Now, type in a filesystem type that you want to use for the partition. I will go for ext4.

NOTE: You can find out what keywords you can use here with the following command:

$ grep -v nodev /proc/filesystems| cut -f2

Now, type in the location in megabyte (MB) where the partition starts. If it’s the first partition, then 1 (MB) is an acceptable value. Once you’re done, press <Enter>.

Now, type in the location in megabyte (MB) where the partition ends. The size of the partition will be the difference between the End and Start location. For example, let’s say, you want to create a 1GB/1024MB partition. So, the end will be 1024. Once you’re done, press <Enter>.

NOTE: You can’t put 1025 here due to alignment problems. Parted don’t align partitions automatically.

The partition will be created.

You can list all the partitions of your selected storage devices as follows:

As you can see, the newly created partition is listed.

NOTE: When you create multiple partitions with parted, you have to start the new partition from at least End+1 of the last partition. For example, the partition I created earlier ended in 1024MB. So, the next partition will start from 1025MB or more.

I created another partition to demonstrate how to remove partitions using parted in the next section.

Removing Partitions:

First, list all the partitions of your selected storage device as follows:

Let’s say, you want to delete the partition number 2 as marked in the screenshot below.

To do that, run the following parted command:

As you can see, partition number 2 no longer exists.

Changing the Unit:

When you create a new partition, you have to specify the Start and End section of your new partition. The default unit is MB. You can change it very easily in parted.

The supported units and keywords are:

Unit	keyword
Sectors	s
Bytes	B
Cylinders	cyl
cylinders, heads, sectors	chs
Kilobytes	KB
Mebibytes	MiB
Megabytes	MB
Gibibytes	GiB
Gigabytes	GB
Percentage	%

NOTE: For more information on this, check the man page of parted with the following command:

You can use the unit command to change the default unit.

For example, let’s say you want to change the default unit MB to sectors, then run the following command:

As you can see, the display unit has changed as well.

Now, you can also create partitions with the newly set unit.

So, that’s how you use parted on Linux. Thanks for reading this article.

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You’ve found your way to our 24-day-long Linux command-line toys advent calendar. If this is your first visit to the series, you might be asking yourself what a command-line toy even is. It could be a game or any simple diversion that helps you have fun at the terminal.

Some of you will have seen various selections from our calendar before, but we hope there’s at least one new thing for everyone.

There are many ways to listen to music at the command line; if you’ve got media stored locally, cmus is a great option, but there are plenty of others as well.

Lots of times when I’m at the terminal, though, I’d really rather just zone out and not pay close attention to picking each song, and let someone else do the work. While I’ve got plenty of playlists that work for just such a purpose, after a while, even though go stale, and I’ll switch over to an internet radio station.

Today’s toy, MPlayer, is a versatile multimedia player that will support just about any media format you throw at it. If MPlayer is not already installed, you can probably find it packaged for your distribution. On Fedora, I found it in RPM Fusion (be aware that this is not an “official” repository for Fedora, so exercise caution):

$ sudo dnf install mplayer

MPlayer has a slew of command-line options to set depending on your situation. I wanted to listen to the local college radio station here in Raleigh (88.1 WKNC, they’re pretty good!), and so after grabbing the streaming URL from their website, all that took to get my radio up and running, no GUI or web player needed, was:

$ mplayer -nocache -afm ffmpeg http://wknc.sma.ncsu.edu:8000/wknchd1.mp3

MPlayer is open source under the GPLv3, and you can find out more about the project and download source code from the project’s website.

As I mentioned in yesterday’s article, I’m trying to use a screenshot of each toy as the lead image for each article, but as we moved into the world of audio, I had to fudge it a little. So today’s image was created from a public domain icon of a radio tower using img2txt, which is provided by the libcaca package.

Do you have a favorite command-line toy that you we should have included? Our calendar is basically set for the remainder of the series, but we’d still love to feature some cool command-line toys in the new year. Let me know in the comments below, and I’ll check it out. And let me know what you thought of today’s amusement.

Be sure to check out yesterday’s toy, Let you Linux terminal speak its mind, and come back tomorrow for another!

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Bash `yes` command is one of those commands of Linux that is related to the operation of another command. Using this command is useless when you execute the command independently. By default, `yes` command repeats the character ‘y’ if no string value is specified with this command. When `yes` command uses with pipe and another command then it will send the value ‘y’ or `yes` for any confirmation prompt. This command can help to save time by doing many confirmation tasks automatically.

You can use `yes` command with an option or any string value, but both are optional for this command.

yes [OPTION]

yes [STRING]…

Options

This command has not more options. Two options of this command are mentioned below.

–version

It is used to display the installed version of this command.

–help

It is used to get detail information of this command.

Example#1:

When you run the `yes` command without any option and string value then it will print ‘y’ for infinite times.

Output:

The following output will appear.

Example#2:

When you run the `yes` command with a specific string value then it will print the string value for infinite times.

Output:

The following output will appear.

Example#3:

`cp` command is used in bash to create any new file by copying an existing file. If the new filename exists then it will ask for overwrite permission if you run cp command with -i option. In this example, two text files hello.txt and sample.txt are used. If these two text files exist in the current location and `cp` command is run for copying sample.txt to hello.txt with -i option then it will ask for overwrite permission.

$ cat hello.txt
$ cat sample.txt
$ cp -i sample.txt hello.txt

You can use `yes` command to prevent from overwriting the existing file or forcefully overwrite the existing file. In the following commands, the first command is used to prevent the overwrite and the second command is used to overwrite the file without any permission.

$ yes n | cp -i sample.txt hello.txt
$ yes | cp -i sample.txt hello.txt

Output:

Example#4

You can use `yes` command to run any script multiple times in the command line. In this example, `yes` command is used to run while loop repeatedly ten times. Here, `yes` command will continuously send the numeric value from 1 to 10 to the loop and the loop will print the values in regular interval of one second.

$ yes “$(seq 1 10)” | while read n; do echo $n; sleep 1; done

Output:

Example#5:

You can use `yes` command to send any string value to a script while executing the script file. Create a bash file named ‘yes_script.sh’ and add the following script. If you run the script using `yes` command with empty string then it will print “Empty value is passed by yes command” otherwise it will print the string value send by `yes` command by combining with other string.

#!/bin/bash

#Read the value passed from yes commandread string

#check the string value is empty or notif [ “$string” == “” ]; then

echo “Empty value is passed by yes command”

elsenewstr=”The value passed by yes command is $string”

echo $newstr
fi

Run the `yes` command with an empty string and the bash script file, yes_script.sh.

$ yes “” | bash yes_script.sh

Output:

Run the yes command with a string value, “testing” and the bash script file, yes_script.sh.

$ yes testing | bash yes_script.sh

Output:

Example#6:

You can use `yes` command for the testing purpose also. You can run the following command to create a file with a huge amount of data for testing. After executing the command, a file named ‘testfile’ will be created that will contain 50 lines with the content, ‘Add this line for testing’.

$ yes ‘Add this line for testing’ | head -50 > testfile

Output:

Conclusion

The basic uses of `yes` command are shown in this tutorial by using different types of examples. It is a very useful command when you are confirmed about any task and don’t want to waste time for unnecessary confirmation. You can use this command for some advanced level tasks, such as comparing processors ability or the loading capacity of any computer system etc.

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Quoting is used to disable the special meaning of the special characters. There are many shell metacharacters which have specific meanings. But when you need to represent those characters then it will require to remove the special meaning of those characters and it is done by quoting the character. You can do this task by using three ways. These are escape characters, single quotes and double quotes which are explained with examples in this tutorial.

Bash escape character is defined by non-quoted backslash (). It preserves the literal value of the character followed by this symbol. Normally, $ symbol is used in bash to represent any defined variable. But if you use escape in front of $ symbol then the meaning of $ will be ignored and it will print the variable name instead of the value. Run the following commands to show the effects of escape character ().

Example#1:

The meaning of `pwd` command is to display the current working directory path. In the following example, the value of the `pwd` command is stored in a variable. When symbol is used in front of $ symbol then the variable name will print instead of the value.

$ pd=`pwd`
$ echo $pd
$ echo $pd

Output:

Single quotes:

When you enclose characters or variable with single quote ( ‘ ) then it represents the literal value of the characters. So, the value of any variable can’t be read by single quote and a single quote can’t be used within another single quotes. Some examples of single quote are shown below.

Example#2:

In this example, a string value is stored in the variable $var. `echo` command prints the value of this variable without any quotation. When the variable is quoted by single quote then the variable name will print as output. If the backslash ( ) is used before the single quote then the value of the variable will be printed with single quote.

$ var=’Bash Scripting Language’
$ echo $var
$ echo ‘$var’
$ echo ‘$var’

Output:

Example#3:

Sometimes it is required to print a single quote inside a string. A single quoted string can’t contain another single quote inside the string. You can do this task by adding backslash in the front of single quote. In the following example, single quote of don’t word is printed by using backslash.

$ var=$’I don’t like this book’
$ echo $var

Output:

Example#4:

backticks is not supported by single quotes. In this example, calendar value is stored into a variable, $var. The value of this variable will print properly by echo command if you don’t use any quotation. But when the variable is quoted by single quote in echo command then it prints the variable name instead of the value of the variable.

$ var=`cal`
$ echo $var
$ echo ‘$var’

Output:

Double quotes

Double quotes ( ” ) is another way to preserve the literal value of the characters. The dollar sign ( $ ) and backticks ( ` ) characters can able to keep their special meaning within double quotes. Backslash ( ) can also retain its value when it is used by following backticks, double quote and backslash. Some examples of double quotes are shown below.

Example#5:

One limitation of the single quote is that it can’t parse the value of the variable within the quotation. In this example, a string value is assigned to a variable named, $var and print the value of that variable using double quotation in echo command.

$ var=’server-side scripting language’
$ echo “PHP is a $var”

Output:

Example#6:

Any command output can be printed by using double quotation. In the following example, date command is enclosed by double quotation and printed by using double quotation.

Output:

Example#7:

You can’t use double quotation within another double quotation to assign any string value. If you want to print double quote in the output then you have to use the backslash () with the string. In a similar way, you can print backticks (`) and backslash() characters in the output by using the backslash() within the double quotation. In this example, the first command will print “500” with the double quotation, the second command will print `date` with backticks and the third command will print “PHP” with backslash.

$ echo “The price is “500””
$ echo “`date` command is used for date value”
$ echo “\PHP\ is a programming language”

Output:

Example#8:

Double-quoted and single-quoted strings work same when they are used together without any space in a print command. But if you use any space between the string values then they will treat as separate value and print separately. In this example, three double-quoted strings are used in the first printf command. These strings will combine together and print as a single string when you will run the command. Two single-quoted and one double-quoted strings are used in the second print command and it will work like the first print command. Three double-quoted strings with space are used in the third print command and each string value will work as a separate string and print each string in a newline.

$ printf ‘%sn’ “Ubuntu””LinuxMint””Fedora”
$ printf ‘%sn’ ‘Ubuntu'”LinuxMint”‘Fedora’
$ printf ‘%sn’ “Ubuntu” “LinuxMint” “Fedora”

Output:

Example#9:

Create a bash file named escape.sh, and add the following code. In this example, a text data with double quotes and dollar sign is used. It is shown earlier that double quote and dollar symbol can’t print within a string enclosed by double quotation. So, the backslash is added in front of the double quotes and dollar symbol to print these. Here, a for loop is used to iterate the string variable, $string and print each word of the text that is stored in that variable.

#!/bin/bash

#Initialize the variable with special characterstring=”The price of this “book” is $50″

#Iterate and print each word of the string variablefor word in $string

doecho $word

done

Run the script.

Output:

Conclusion

Hope, this tutorial will help you to use escape characters, single quote and double quote based on the requirements of your script.

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The full form of JDK is Java Development Kit. It is used to write and test Java programs. Recently, JDK 11 came out. It is the latest version of JDK LTS (Long Term Support) release.

In this article, I will show you how to install Oracle JDK 11 on Ubuntu. I will be using Ubuntu 18.04 LTS for the demonstration. But it should work on any LTS version of Ubuntu. So, let’s get started.

Oracle JDK 11 is not available in the official package repository of Ubuntu. But you can easily download it from the official website of Oracle and install it on Ubuntu.

First, visit the official page of Java SE at https://www.oracle.com/technetwork/java/javase/overview/index.html

Once the page loads, click on Downlaods as marked in the screenshot below.

Now, from the Java SE 11.x (LTS) section, click on DOWNLOAD as marked in the screenshot below. At the time of this writing, the latest version of JDK 11 is 11.0.1.

Now, scroll down a little bit and click on Accept License Agreement as marked in the screenshot below.

Now that you’ve accepted the Oracle Technology Network License Agreement for Oracle Java Standard Edition, you are ready to download Oracle JDK 11. To download Oracle JDK 11 for Ubuntu, click on the DEB file link as marked in the screenshot below.

Your browser should prompt you to save the Oracle JDK 11 DEB package file. Select Save File and click on OK.

Your download should start. It may take a while to finish.

Installing Oracle JDK 11:

Once the download is complete, navigate to the directory where your browser saved the DEB package file. Usually, it is the ~/Downloads directory in your login users HOME directory.

As you can see, jdk-11.0.1_linux-x64_bin.deb package file is there.

NOTE: The package file name may be different by the time you read this article. Make sure you replace the package file name with yours from now.

Now, install Oracle JDK 11 with the following command:

$ sudo dpkg -i jdk-11.0.1_linux-x64_bin.deb

Now, type in your login user’s password and press <Enter>.

Oracle JDK 11 should be installed.

Adding Oracle JDK 11 to the PATH:

The Oracle JDK 11 DEB package file installs Oracle JDK 11 in /usr/lib/jvm directory. It is not in the PATH by default. So, we have to manually add it to the PATH of Ubuntu.

First, find out the directory name where the Oracle JDK 11 is installed with the following command:

As you can see, the directory name is jdk-11.0.1/ in my case. It may be different for you. Make sure to replace it with your from now on.

Now, create a new file /etc/profile.d/jdk11.sh with the following command:

$ sudo nano /etc/profile.d/jdk11.sh

An empty file should be opened.

Now, add the following lines to the file.

export JAVA_HOME=”/usr/lib/jvm/jdk-11.0.1″
export PATH=”$PATH:$/bin”

NOTE: Make sure you change jdk-11.0.1 to the directory name you have.

Finally, the file looks as follows. Now, press <Ctrl> + x and then press y followed by <Enter> to save the file.

Now, restart your computer with the following command:

Once your computer boots, open a Terminal and run the following commands to verify whether JAVA_HOME variable is correctly set and Oracle JDK 11 is on the PATH.

$ echo $JAVA_HOME
$ echo $PATH

As you can see, JAVA_HOME and PATH variables are correctly set.

Now, run the following command to check whether JDK 11 is working.

As you can see, I can run the javac binary without any problem. So, JDK 11 is working.

Compiling a Java Program with Oracle JDK 11:

Now, I am going to write a simple java program to test whether we can compile and run it with Oracle JDK 11.

Now, create a file Hello.java and type in the following lines in it.

public class Hello {
public static void main(String[] args) {
System.out.println(“Welcome to LinuxHint!”);
}
}

Now, to compile Hello.java source file, open a Terminal and navigate to the directory where your Hello.java source file is saved and run the following command:

A new file Hello.class should be generated as you can see in the screenshot below. It is called a Java class file. Java class file contains Java bytecodes that the JVM (Java Virtual Machine) can run.

Now, run Hello.class Java class file as follows:

NOTE: Type in only the filename without .class extension. Otherwise, it won’t work.

The correct output is displayed as you can see in the screenshot below.

So, that’s how you install Oracle JDK 11 on Ubuntu. Thanks for reading this article.

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How to install Node.js with npm on CentOS 7

Install Node.js with npm on CentOS

In this tutorial, we are going to learn how to install Node.js with npm on CentOS. Node.js is the opensource JavaScript Run-time environment for server-side execution of JavaScript code. Node.js built on Chrome’s V8 JavaScript engine so it can be used to build different types of server-side application.

Where npm stands for Node Package Manager which is the default package manager for Node.js. npm is the worlds largest software registry for Node.js packages with thousands of packages available.

in this tutorial we will install Node.js in following two ways:

1. Install Node.js and npm using EPEL repository
2. Install Node.js and npm using nvm

Prerequisites

Before you start to install Node.js and npm on CentOS 7. You must have the non-root user account on your server with sudo privileges.

1. Install Node.js and npm using EPEL repository

First you will need to add NodeSource yum repository on your system. Add it by using curl running following command.

curl -sL https://rpm.nodesource.com/setup_10.x | sudo bash –

NOTE : The latest LTS version of Node.js is 10.x if you want to install 8.x version then just replace setup_10.x with setup_8.x

After executing above command NodeSource repository is enabled. Now you can install Node.js by using the following command. When it will prompt you to retrieve GPG key just press ‘y’ to continue.

sudo yum install nodejs

Now confirm the installation of Node.js by using the following command

node –version

And confirm npm installation with the following command

npm –version

2. Install Node.js and npm using NVM

NVM stands for Node Version Manager which is used to manage multiple Node.js versions. If you want to install or uninstall different versions of Node.js then NVM is there for you.

First, we will install NVM (Node Package Manager) on your system. So download NVM installation script running the following command.

curl -o- https://raw.githubusercontent.com/creationix/nvm/v0.33.11/install.sh | bashHow to install Node.js and npm using nvm on CentOS 7

As shown in the above output you should close and reopen terminal.

Check nvm version and confirm installation typing

node –version

Now install Node.js by using the following command.

nvm install node

Verify Node.js installation by typing

node –version

The output should be:

Output

v10.14.0

You can install multiple versions of Node.js. To do so type following:

nvm install 8.14nvm install –ltsnvm install 11.3

To list all the versions installed run following command.

nvm ls

You can change the current default version of Node.js by using the following command.

nvm use 8.14

To uninstall a Node.js version type following command

nvm uninstall 11.14

Conclusion

You have successfully learned how to install Node.js with npm on CentOS 7. If you have any queries regarding this please don’t forget to comment below.

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If you happen to use KDE as your preferred graphical desktop, Konbini might be right up your alley. It adds several useful image manipulation actions to the Dolphin file manager as well as installs and configures a handful of photography-related tools.

The supplied installer does the donkey job of fetching and installing the required pieces. It also adds the dedicated Konbini item to the right-click context menu in Dolphin. This menu gives you quick access to several useful commands that let you recompress and resize the currently selected image file, rename the file using date and time values extracted from its EXIF metadata, quickly geotag the selected photo, show the selected geotagged photo on OpenStreetMap, and more.

Installing Konbini is supremely easy. In the Terminal, run the curl -sSL https://is.gd/konbini | bash command for the installer to finish. The installer script is designed for use with openSUSE, Ubuntu, and Debian. But it can be easily modified to work with other Linux distributions.

In the template folder in the konbini directory you’ll find example files that you can use to create your own actions. Let’s say you want to create an action that uploads the currently selected photo to an FTP server. First, rename the example file in the template/script folder to something more descriptive like upload-ftp. Open the file for editing, remove the existing commands, and add the following code (replace the example values with the actual FTP server address or domain name, user name, and password):

curl -T “$file” ftp://ftp.example.com/path/to/dir/ –user user:password
notify-send “It works!”

Save the changes, then move the file to the /usr/local/bin/ directory, and make the script executable:

sudo mv upload-ftp /usr/local/bin/
sudo chown root:root /usr/local/bin/upload-ftp
sudo chmod 755 /usr/local/bin/upload-ftp

Next, rename the example.png icon in the template/icon folder to upload-ftp.png and move it to the /usr/share/icons/konbini-icons/ directory:

mv upload-ftp.png /usr/share/icons/konbini-icons/

Instead of the supplied generic example icon, you can use a more appropriate icon from the Feather Icons set.

Finally, rename the example.desktop file in the template/desktop folder to upload-ftp.desktop, open it for editing and replace the example values:

[Desktop Entry]
Type=Service
X-KDE-Priority=TopLevel
X-KDE-Submenu=Konbini
ServiceTypes=KonqPopupMenu/Plugin
MimeType=image/jpeg;image/JPG;image/JPEG;image/jpg;
Actions=UploadFTP
[Desktop Action UploadFTP]
Name= Upload via FTP
Exec=/usr/local/bin/upload-ftp %f
Icon=/usr/share/icons/konbini-icons/upload-ftp.png

Save the changes, and move the file to the /usr/share/kservices5/ServiceMenus directory:

mv upload-ftp.desktop /usr/share/kservices5/ServiceMenus/

Launch Dolphin, right-click on a JPEG image, and you should see the newly-added action in the Konbini menu.

This is an excerpt from the Linux Photography book. Get your copy from Google Play Store or Gumroad.

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