On Linux and Unix-based operating systems, pipes are very useful since they are a simple way to achieve IPC (inter-process communication). When we connect two processes in a pipeline, the output of the first one is used as the input of the second one. To build a so called “anonymous” pipe, all we have to do is to use the | operator. Anonymous, or unnamed pipes last just as long as the processes they connect. There is, however, another type of pipe we can use: a FIFO, or named pipe. In this article we will see how named pipes work and in what they are different from the standard pipes.
If you are just starting to explore the Bash coding language, you will soon find yourself wanting to create conditional statements. Conditional statements, in other words, define ‘if a condition is true or false, then do this or that, and if the opposite is true, do something else’. This is the most basic function of any conditional statement.
This article will introduce you to the five basic if statement clauses. being if, elif, else, then and fi. The first simply opens a if statement, the then introduces the what commands to execute if the statement condition was true section and the else introduces the what commands to execute if the statement condition was false section. Finally, the fi closes the statement. We also have the special elif on which we will see more in a minute. Let’s start with an easy example.
In this tutorial you will learn:
How to implement an if statement at the Bash command line
How such if statements can also be used inside a Bash scripts
Examples showing you the if, elif, else, then and fi clauses in Bash
As sever optimal use/maximization continues to grow, it becomes more and more important to manage processes well. One aspect of this is automatic process termination. When a process has gone rogue, and is consuming too much resources, it can be terminated automatically.
This is especially suited to servers which have a lot of temporary or disposable processes. It is also well suited for testing servers which are running many test trials and where such test trials prove to be unstable or cause the software under testing to behave erratically (for example by using too much memory)
In this tutorial you will learn:
How to manage processes in an automated fashion
Which resources you may want to monitor, and why
Example code showing how automatic process termination can work for memory hogging issues
If you have ever used Bash subshells ($(...)), you know how flexible subshells can be. It only takes a few characters to start a subshell to process anything required, inline to another statement. The number of possible use cases is virtually unlimited.
We can also use Bash subshells inside if statements, inline with the statement. Doing so gives the user and developer much additional flexibility when it comes to writing Bash if statements.
In general, one may use the time Bash utility (see man time for more information) to run a program, and obtain runtime duration and system resource usage summaries. But how can one time particular sections of code, directly from within the Bash source code?
Using some easy variable assignments and calculations, it is possible to achieve accurate timing metrics for Bash script executions.
In this tutorial you will learn:
How to time Bash scripts using variable assignments and calculations
How to use overlapping timers to time specific sections of your scripts
Examples which exemplify how specific sections of code can be timed
In our automation scripts we often need to launch and monitor external programs to accomplish our desired tasks. When working with Python, we can use the subprocess module to perform said operations. This module is part of the programming language standard library. In this tutorial we will take a quick look at it, and we will learn the basics of its usage.
In this tutorial you will learn:
How to use the “run” function to spawn an external process
How to capture a process standard output and standard error
How to check the exist status of a process and raise an exception if it fails
How to execute a process into an intermediary shell
How to set a timeout for a process
How to use the Popen class directly to pipe two processes
CSV is the acronym of “Comma Separated Values”. A csv file is a just plain text document used to represent and exchange tabular data. Each row in a csv file represents an “entity”, and each column represents an attribute of it. Columns are usually separated by a comma but other characters can be used as field separator instead of it. In this tutorial we will see how to read and create csv files using Python and specifically the csv module, which is part of the language standard library.
In this tutorial you will learn:
How to read csv rows as a list of strings
How to read a csv as a list of dictionaries
How to create a csv using Python
How to create a csv starting from a list of dictionaries
grep is a versatile Linux utility, which can take a few years to master well. Even seasoned Linux engineers may make the mistake of assuming a given input text file will have a certain format. grep can also be used, directly in combination with if based searches to scan for the presence of a string within a given text file. Discover how to correctly grep for text independent of character sets, how to use the -q option to text for string presence, and more!
In this tutorial you will learn:
How to do correct character set-independent text searches with grep
How to use advanced grep statements from within scripts or terminal oneliner commands
How to test for string presence using the -q option to grep
Examples highlighting grep usage for these use cases
Whenever we work with textual strings, sooner or later the issue of case comes up. Does a word need to be fully uppercase, fully lowercase, with a capitalized letter at the start of the word or sentence, and so on.
An idiom is a natural language expression of a simple programming task. For example, in the sleep 10 command (which will pause the terminal one is working in for ten seconds), the word sleep is a natural language expression of what is a time based coding construct, developed in the Bash GNU coreutils software package.
There are a number of special variable-bound idioms (i.e. suffixes which can be added to a variable name, indicating what we would like to do with a given variable), which can be used in Bash to more easily do these types of conversions on the fly instead of having to use for example the Sed Stream Editor with a Regular Expression to do the same.
This makes working with variables that need case modification, or if statement testing a whole lot easier and provides great flexibility. Idioms can be added directly inside the if statements and do not need to employ a subshell with sed.
While the syntax looks slightly complex to start with, once you learn a little mental support trick to remember the right keys, you will be well on your way to use these idioms in your next script or Bash one-liner script at the command line!
In this tutorial you will learn:
How to use the ^, ^^, , and ,, Bash variable suffix idioms
How to use a regular expression [] range idiom in combination with these
How to use the ^ and , idioms directly from within if statements
Detailed examples exemplifying the use of ^, ^^, , and ,,
This tutorial will explain the Bash string concatenation by using examples. When it comes to bash scripting or programming in general, the concatenation refers to joining two or more string together to produce single unified output. Using Bash shell and bash scripting the string concatenation can be achieved in number for ways.
Decimal calculations are sometimes required in Bash. The standard calculation Bash programming idiom ($[]) is unable to provide a decimal output. Whilst we can trick it into calculating (but not generating) a decimal output by multiplying the numbers by for example a factor of 1000 and then doing an text based splitting, this is a ugly workaround and creates complex code. There is however a utility in Bash which can natively do decimal based calculations without any tricks or workarounds!
In this tutorial you will learn:
How to use bc to perform decimal calculations
How to make decimal based calculations at the Bash command line or from in your scripts
How to use variables to store the results produced by bc
In this article we have a look at obtaining some basic hardware, system and operating system configuration information directly from the command prompt in your terminal. Having this information, and knowing where to find it, often helps when configuring a system, researching optimal hardware and software solutions, and generally being in control of the Linux system you own or manage.
We will focus mostly on every day information, the kind that is required on a regular basis. Going more in-depth often requires a few online searches to first define alignment better, and then often requires additional skills to interpret the results or output shown.
For example, we will not be looking at the output of vmstat, though we will discover how to find out what CPU is in your system without opening the hood. We will also look at some basic resource limit variables and surrounding concerns. The target audience for this article is thus beginner to medium advanced.
In this series, we discuss various ideas and practical approaches for handling big data, or more specifically handling, transforming, mangling, munging, parsing, wrangling, transforming and manipulating the data at the Linux command line.
This third article in the series will continue explore Bash tools which can help us when processing and manipulating text-based (or in some cases binary) big data. As mentioned in the previous articles, data transformation in general is an semi-endless topic as there are hundreds of tools for each particular text format. Remember that at times using Bash tools may not be the best solution, as an off-the-shelf tool may do a better job. That said, this series is specifically for all those (many) other times when no tool is available to get your data in the format of your choice.
Finally, if you want to learn more about why big data manipulation can be both fun and profitable… please read Part 1 first.
In this tutorial you will learn:
Additional big data wrangling / parsing / handling / manipulation / transformation techniques
What Bash tools are available to assist you, specifically for text based applications
Various examples, showing different methods and approaches
Vim needs no presentations: it is probably the most loved text editor by system administrators, also due to the fact that it is a clone and an improvement of the original Vi, which is included by default in practically all Linux and Unix based operating systems. Vim can be quite intimidating at first, and it has a steep learning curve; learning how to use it, however, can really increase our productivity. In this article we will learn the Vim basics.
In this tutorial you will learn:
How to install Vim
Why Vim is a “modal” text editor and what are the Vim modes
How to tweak Vim look and feel using the ~/.vimrc configuration file
The Bash command line provides nearly limitless power when it comes to executing nearly anything you want to do. Whether it is processing a set of files, editing a set of documents, handling big data, managing a system or automating a routine, Bash can do it all.
This tutorial is sure to arm you with the tools and methods you need to become a much more proficient Bash user. Even already advanced users will likely pickup something new and exciting.
