O'Reilly's bestselling book on Linux's bash shell is at it again. Now that Linux is an established player both as a server and on the desktop Learning the bash Shell has been updated and refreshed to account for all the latest changes. Indeed, this third edition serves as the most valuable guide yet to the bash shell.As any good programmer knows, the first thing users of the Linux operating system come face to face with is the shell the UNIX term for a user interface to the system. In other words, it's what lets you communicate with the computer via the keyboard and display. Mastering the bash shell might sound fairly simple but it isn't. In truth, there are many complexities that need careful explanation, which is just what Learning the bash Shell provides.If you are new to shell programming, the book provides an excellent introduction, covering everything from the most basic to the most advanced features. And if you've been writing shell scripts for years, it offers a great way to find out what the new shell offers. Learning the bash Shell is also full of practical examples of shell commands and programs that will make everyday use of Linux that much easier. With this book, programmers will learn:
If you do not have Linux installed or you are just starting out, you can easily access the Linux command line through Replit. Replit is a browser-based IDE where you can access the bash shell in a few minutes.
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A bash script is a file containing a sequence of commands that are executed by the bash program line by line. It allows you to perform a series of actions, such as navigating to a specific directory, creating a folder, and launching a process using the command line.
Bash scripting is a powerful and versatile tool for automating system administration tasks, managing system resources, and performing other routine tasks in Unix/Linux systems. Some advantages of shell scripting are:
The term "shell" refers to a program that provides a command-line interface for interacting with an operating system. Bash (Bourne-Again SHell) is one of the most commonly used Unix/Linux shells and is the default shell in many Linux distributions.
Although Bash is a type of shell, there are other shells available as well, such as Korn shell (ksh), C shell (csh), and Z shell (zsh). Each shell has its own syntax and set of features, but they all share the common purpose of providing a command-line interface for interacting with the operating system.
Bash scripts start with a shebang. Shebang is a combination of bash # and bang ! followed by the bash shell path. This is the first line of the script. Shebang tells the shell to execute it via bash shell. Shebang is simply an absolute path to the bash interpreter.
The script first prompts the user to enter a number. Then, it uses an if statement to check if the number is greater than 0. If it is, the script outputs that the number is positive. If the number is not greater than 0, the script moves on to the next statement, which is an if-elif statement. Here, the script checks if the number is less than 0. If it is, the script outputs that the number is negative. Finally, if the number is neither greater than 0 nor less than 0, the script uses an else statement to output that the number is zero.
In Bash, case statements are used to compare a given value against a list of patterns and execute a block of code based on the first pattern that matches. The syntax for a case statement in Bash is as follows:
The double semicolon ";;" separates each block of code to execute for each pattern. The asterisk "*" represents the default case, which executes if none of the specified patterns match the expression.
In this example, since the value of "fruit" is "apple", the first pattern matches, and the block of code that echoes "This is a red fruit." is executed. If the value of "fruit" were instead "banana", the second pattern would match and the block of code that echoes "This is a yellow fruit." would execute, and so on. If the value of "fruit" does not match any of the specified patterns, the default case is executed, which echoes "Unknown fruit."
Cron is a powerful utility for job scheduling that is available in Unix-like operating systems. By configuring cron, you can set up automated jobs to run on a daily, weekly, monthly, or specific time basis. The automation capabilities provided by cron play a crucial role in Linux system administration.
Debugging and troubleshooting are essential skills for any Bash scripter. While Bash scripts can be incredibly powerful, they can also be prone to errors and unexpected behavior. In this section, we will discuss some tips and techniques for debugging and troubleshooting Bash scripts.
One of the most useful techniques for debugging Bash scripts is to set the set -x option at the beginning of the script. This option enables debugging mode, which causes Bash to print each command that it executes to the terminal, preceded by a + sign. This can be incredibly helpful in identifying where errors are occurring in your script.
When Bash encounters an error, it sets an exit code that indicates the nature of the error. You can check the exit code of the most recent command using the $? variable. A value of 0 indicates success, while any other value indicates an error.
Another useful technique for debugging Bash scripts is to insert echo statements throughout your code. This can help you identify where errors are occurring and what values are being passed to variables.
If you want your script to exit immediately when any command in the script fails, you can use the set -e option. This option will cause Bash to exit with an error if any command in the script fails, making it easier to identify and fix errors in your script.
In this article, we started with how to access the terminal and then ran some basic bash commands. We also studied what a bash shell is. We briefly looked at branching the code using loops and conditionals. Finally, we discussed automating the scripts using cron followed by some troubleshooting techniques.
To participate in this Library Carpentry lesson, you will need aworking Unix-like shell environment. We will be using Bash (Bourne AgainShell) which is standard on Linux and macOS. Some macOS users(Catalina or later) will have zsh (Z shell) as their default version.Even if you are a Windows user, learning Bash will open up a powerfulset of tools on your personal machine, and familiarize you with thestandard remote interface used on most servers and supercomputers.
Linux: The default shell is usually Bash, but ifyour machine is set up differently you can run it by opening a terminaland typing bash followed by the enter key. Thereis no need to install anything. Look for Terminal in your applicationsto start the Bash shell.
macOS: Open Terminal from/Applications/Utilities or Spotlight Search. In versionsbefore Catalina, Bash is the default shell, so you do not need to doanything further. In Catalina and onwards, the default shell is zsh,which is similar but may behave differently from Bash in some cases. Toswitch to Bash, enter the command bash in your terminalwindow followed by the enter key.
Windows: On Windows, CMD or PowerShell arenormally available as the default shell environments. These use a syntaxand set of applications unique to Windows systems and are incompatiblewith the more widely used Unix utilities. However, a Bash shell can beinstalled on Windows to provide a Unix-like environment. For this lessonwe suggest using Git Bash, part of the >Git for Windows package:
There are also some more advanced solutions available for runningBash commands on Windows. A Bash shell command-line tool is availablefor Windows 10, which you can use if you enable the WindowsSubsystem for Linux. You can also run Bash commands on a remotecomputer or server that already has a Unix Shell from your Windowsmachine. This can be done through a Secure Shell (SSH) client. Oneclient available for free for Windows is PuTTY.
This command will show you where you are in your file system, whichshould now be your home directory. In the lesson, you will find out moreabout the commands ls, pwd and how to workwith the data in shell-lesson folder.
Ok, so you want to learn how to write Bash scripts on Unix/Linux. Or, it's part of a subject you're doing and so you're learning because you have to. Either way, that's great. Keep on reading my friend as you are about to harness a powerful tool that will allow you to perform complex repetitive tasks with minimal effort.
The following pages are intended to give you a solid foundation in how to write Bash scripts, to get the computer to do complex, repetitive tasks for you. You won't be a bash guru at the end but you will be well on your way and armed with the right knowledge and skills to get you there if that's what you want (which you should).
Bash scripts are used by Systems Administrators, Programmers, Network Engineers, Scientists and just about anyone else who uses a Linux/ Unix system regularly. No matter what you do or what your general level of computer proficiency is, you can generally find a way to use Bash scripting to make your life easier. Bash is a command line language. The name stands for Bourne Again SHell. It is an open source version of the Bourne Shell and was first released in 1989.
This Bash scripting tutorial is divided into 8 sections. In general I recommend you work through them in order but if you've come here just to learn about a specific topic then who am I to slow you down, just head straight on over.
The best way to learn Bash Scripting is as a series of small, easy to manage steps. This tutorial is organised as such, with each section building upon the knowledge and skills learned in the previous sections. If you work through them in order, read them fully (there is a fair bit of material but it is important for getting a proper understanding) and practice on the command line as you go I believe you should have a fairly pleasant and smooth journey to Bash scripting mastery. 152ee80cbc
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