Introduction

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Introduction

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Systemd service unit

[Unit]
After=mysql.service

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

[Install]
WantedBy=default.target

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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.

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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.

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$ cat bash-127.sh 
#bin/bash

non-existing-command
echo $?

$ ./bash-127.sh 

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

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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.

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$ cat file.txt
line1 4.5
line2 6

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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.

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#!/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'))

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About

Configuration

Usage

# docker pull linuxconfig/cran-r

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from sys import argv

name, first, second, third, fourth = argv

print "Script name is:", name
print "Your first argument is:", first
print "Your second argument is:", second
print "Your third argument is:", third
print "Your fourth argument is:", fourth


# Alternatively we can access "argv" argument list directly using range. For exmaple:

# Print all arguments except script name
print argv[1:]

# Print second argument
print argv[2]

# Print second and third argument
print argv[2:4]

# Print last argument
print argv[-1]

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$ python
Python 2.7.5 (default, Jun 24 2015, 00:41:19) 
[GCC 4.8.3 20140911 (Red Hat 4.8.3-9)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> print u"\u041b"
Л

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print "What is your name?"
name = raw_input()
print "Hello %s!" % name 

$ python input.py 
What is your name?
Monty Python
Hello Monty Python!

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