Introduction

Obviously working with numbers in programming is important. Python as excellent mathematical capabilities, and there are tons of additional libraries available to extend Python's built in functionality for even the most advanced calculations. Of course, the basics are important too, and numbers and some basic calculations come into play when controlling the flow of programs and making selections. That's why knowing your way around working with numbers in Python is especially important.

Introduction

Do you remember variables from math class in school? Variables in programming are actually very similar. Variables are just symbols that that represent a value and that value can be changed; thus the name variable. Unlike in math, variables in programming can be much more free form. Variables don't just have to be a letter. Variables can be a single character, but they are more commonly a word or a short descriptive phrase in lower case with words separated by underscores. It's actually best to name variables something descriptive so the you and anyone else that you're working with knows exactly what that variable is, even much later on in the code.

Types of Variables

Python is a dynamic duck typed language. Don't worry too much about the terminology, but that means that Python doesn't force you to specify which types variables are when you create them. Oh yeah, there are types of variables. Even though you don't necessarily have to specify their type when you create them, it's a good idea to know what type you want them to be. Later on, having the wrong type of variable will invariably get you into big trouble.

Introduction

You probably want to jump in and start coding right away. That's a great attitude to have, but it's much better to experiment with the language and your programming environment first. If you've never programmed or never worked with an interpreted language like Python before, it's important to get a feel for the way Python works and start to develop a workflow. One great aspect of Python being interpreted is the ability to write a couple of quick lines of code and test them out in real time. There really isn't much setup beyond what you've already done.

Playing With Numbers

Without knowing anything about the language, you can use Python like a basic calculator. Open up either your .py file or the interpreter. Type in a basic math problem and run it.
>>> 10+25
35

Introduction

Python is an interpreted language, meaning that it is compiled every time that it is run. There are a number of pros and cons when talking about an interpreted language like this.

First, on a positive note, they tend to be easier to debug. They fail immediately when they are run, and tell you what went wrong, which is nice compared to compiled languages like C/C++, which can compile just fine, but fail silently when run.

Interpreted languages are also very portable. All you have to do is install the interpreter on a system, and most code written in that language can run fine, regardless of the operating system. There are some exceptions when dealing with operating system specific code and libraries, but if you've planned for portability, you can work around those situations.

Introduction

Python is a dynamically typed, interpreted, general purpose programming language. It's useful for everything from system scripting, to web applications, to full graphical desktop programs. Because of that, it's no surprise that demand for Python programming skills is only increasing, and top companies like Google, Mozilla, Instagram(Facebook), and Reddit rely on it as part of their core technology stack. Not only that, but Python is a favorite in both academic and scientific circles and is gaining ground in the financial sector. Top universities are even using it to teach programming in their computer science programs.

With all of that said, you'd probably be thinking that Python is something super difficult to learn and only accessible to the elite in the technology field, but you couldn't be more wrong. Python is easy. Python is really easy. In fact, Python is one of the first languages used to teach children to program. Python was designed to be very clear and simple to understand. It reads like plain English, and its syntax makes use of spaces rather than brackets and semicolons, so it always looks clean and uncluttered. It's very difficult, if not impossible, to wright messy Python. This helps out new programmers and programmers new to Python big time because you can always tell what you're looking at, or at least, get a decent sense of what it does. This way, you can look at code examples from established open source projects to get an idea of what professional grade Python looks like and how it's used.

Python and Linux work incredibly well together. It wasn't all that long ago that Python supplanted Perl as the de facto scripting and "glue" language on Linux systems. This means that many scripts and utilities that ship with modern Linux systems are written in Python. As a result, most Linux distributions have Python installed by default, but there is a bit of a catch. There are two current versions of Python. Python 2.7.X and Python 3.X.X are both current. Syntactically, they are very similar, but Python 3 has some features that Python 2 doesn't. That means that they are not entirely compatible and many distributions package them separately. So, your system may have Python 2, but not Python 3 or vice versa. This guide and the others in the series are going to cover Python 3. It is the future of Python, and it's not so bad to go back to Python 2 after you've worked with Python 3.

The following config will discuss a basic example on how to execute shell script during a boot time on systemd Linux. There maybe various reason why you might want to execute shell script during Linux startup like for example to start a particular custom service, check disk space, create a backup etc.

The following example below will serve as a basic template to be later modified to suit your specific needs. In the example below we will check a disk space of a /home/ directory during a boot time and write a report to /root/ directory.

Systemd service unit

First, we need to create a systemd startup script eg.disk-space-check.serviceand place it into /etc/systemd/system/ directory. You can find the example of such systemd startup script below:
[Unit]
After=mysql.service

[Service]
ExecStart=/usr/local/bin/disk-space-check.sh

[Install]
WantedBy=default.target

Introduction

Although you may think that you have learned to master Linux command line with bash shell, there are always some new tricks to learn to make your command line skills more efficient. This article will teach you a few more basic tricks on how to make your life with the Linux command line & bash more bearable and even enjoyable.

Bash Command History Expansion

This section will mostly deal with bash shortcuts in combination with three bash history expansion characters "!", "^" and "#". Bash Command History Expansion character "!" indicates start of history expansion. The "^" is a substitution character to modify a previously run command. The last optional character is "#", which denotes the reminder of the line as a comment.

Repeat last command

$ echo Bash Shortcuts
Bash Shortcuts
$ !!
echo Bash Shortcuts
Bash Shortcuts

!! is probably the easiest and most popular bash shortcut, which simply shows and executes your last entered command.

Introduction

For most of us WEP encryption has become a joke. WPA is quickly going the same way thanks to many tools such as Aircrack-ng. On top of this, wired networks are no strangers to unwanted guests as well. Anyone serious about security should have a good Intrusion Detection system in their toolbox.

There are already some very good IDS's (Intrusion Detection Systems) available. Why would anyone want to re-invent the wheel in Bash??? There are a couple of reasons for this. Obviously Bash scripts can be very light weight. Especially compared to some of the GUI programs that are out there. While programs like Etherape suck us in with pretty colors, they require constant monitoring to know when the network has changed. If you are like most of us, you only use the computer for two things, work and play. By using the system bell to alert for new clients online you can leave this script running and not have to have a constant watch. If you do decide you want to inspect what a suspicious client is doing more closely, you can always open up etherape, wireshark, or your tool of choice. But until you have a problem you can play or work on other things.

Another bonus to this program is that it will only show ip addresses on the networks connected to your computer. If you were hosting a busy server or perhaps downloading the latest Linux distro though a torrent client, an IDS may be flooded with connections. Looking for a new malicious client can be like looking for a needle in a hay stack. While this script may seem simple compared to other IDS's, simplicity can have its perks too.

What you will need

Nmap is required for this script to work. We will not be doing any port scanning. However, to make this script fast we needed something better than a regular ping. Nmap's -sP parameter will only use a ping scan to check if a clients up. There were some variations in how Nmap outputs information between versions. So far this script has only been tested using Nmap 5.00 (Debian Squeeze) and 5.21 (Debian Sid). You may have luck with other distros and versions of Nmap. However, with all the possibilities I could only support a couple at this time.

Let's consider a following back script example. The script returns error value using $? variable.
$ cat bash-127.sh 
#bin/bash

non-existing-command
echo $?
After execution we can see the the actual error message and bash 127 error return code:
$ ./bash-127.sh 

./bash-127.sh: line 3: non-existing-command: command not found
127

Introduction

The aim of this article is to provide an overview of the GNU R programming language. It starts a series of articles devoted to programming with R. Its objective is to present, in an organized and concise manner, the elementary components of the R programming language. It is designed to help you understand R code and write your own. It is assumed that the reader has already some basic programming knowledge of R. If you are not familiar with any of R features it is recommended that you first read A quick GNU R tutorial to basic operations, functions and data structures.

Expressions

An R expression is an elementary component of R code. Expression in R can be:

  • assignment statement;
  • conditional statement;
  • arithmetic expression.

Examples of R expressions:

> y<-100
> if (1==1) 1 else 0
[1] 1
> 100/5
[1] 20

R expression are constructed from objects or functions. It is common to separate them with a new line, however, you can also separate expressions with semicolons as below.

Question:
Is there a way to calculate a average of a single column stored in a text file? For example my file contains:
$ cat file.txt
line1 4.5
line2 6
how do I get 5.25 ?

Question:
How do I print all arguments submitted on a command line from a bash script?

Author: Rares Aioanei

Introduction

Since in our first part of this article we said we expected you, the reader, to have some programming knowledge, in this part we want to help you get a on where C stands in comparison to other programming languages you might know. The choice of those languages was pretty tough because of various criteria, but in the end we stopped at C++, Perl and Python. Since programming languages can be classified in lots of ways (depending on paradigm, syntax or style, for example), we didn't try to find languages that are in the same category as C. Instead, since the aforementioned languages are pretty popular in the Linux world, we chose them, mentioning what every language's place is in the great scheme, what it's generally used for and of course, the differences between them and C. This article will be structured as follows: we'll start with important elements of every language, like variable declaration, typing or structure and compare that with how it's done with C. Thusly we hope to give you an idea about the language before we start. The parts this article is made of will be exactly like the announced structure of this article, to make comprehension easier.

The comparison

Types, operators, variables

C++

C++ was initially named "C with classes", which says a lot about its' relation with C. It is widely seen as a superset of C ( thus C++ the unary increment operator ++ ) , introducing object-oriented programming features. Types are essentially used the same, with bool being introduced in C++ for boolean operations. Basically, when talking about C and C++ differences, most of those come from the OOP concepts C++ has and C does not. For example C++ has operator overloading, an OOP-specific term, which means that an operator may have different implementations depending on the data it's operating on. For example, in C++ you can do this:

 
a << 2

Now, if a is an integer, this will do a bitwise operation on it (left shift by 2), but if a is an output stream, the above line will try to write a '2' to it. This kind of behavior is one of the reason C++ is criticized for allowing poor programming practices. Variables and constants are declared the same way as in C.

The following link will extract all URL's for a given web page.
#!/usr/bin/env python3

# Python Version:  3.4.2
# bs4 version: 4.3.2-2

from urllib.request import urlopen
from bs4 import BeautifulSoup

html = urlopen("http://gnu.org") # Insert your URL to extract
bsObj = BeautifulSoup(html.read());

for link in bsObj.find_all('a'):
    print(link.get('href'))

About

The automated build Docker image of The R Project for Statistical Computing “linuxconfig/cran-r” can be used to instantly deploy R programming software environment on any hosts given that you have docker already installed on your system.

Configuration

The docker image with the R Project is compiled and runs on Debian GNU/Linux system.

Usage

Here we assume that docker is already installed on your system.First pull docker image:
# docker pull linuxconfig/cran-r

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