Shulou(Shulou.com)06/01 Report--

This article mainly introduces how to get started with Bash programming, has a certain reference value, interested friends can refer to, I hope you can learn a lot after reading this article, the following let the editor with you to understand.

One of Unix's initial hopes was to allow everyday users of computers to fine-tune their computers to suit their unique work style. Over the decades, expectations for computer customization have declined, and many users believe that the collection of their applications and websites is their "customized environment." One of the reasons is that the components of many operating systems are not open source and the source code is not available to ordinary users.

But for Linux users, custom programs are possible because the whole system revolves around commands that can be used through the terminal. The terminal is not only an interface for quick commands or in-depth troubleshooting; it is also a scripting environment that reduces your workload by handling daily tasks for you.

How to learn programming

If you've never done any programming before, you may have two different challenges to consider: one is to know how to write code, and the other is to know what code to write. You can learn grammar, but if you don't know what keywords are available in the language, you won't be able to continue. In practice, you need to start learning both concepts at the same time, because you can't learn syntax without a stack of keywords, so you initially use basic commands and basic programming structures to write simple tasks. Once you are familiar with the basics, you can explore more programming languages so that your program can do more and more important things.

In Bash, most of the keywords you use are Linux commands. The syntax is Bash. If you have used Bash frequently, the transition to Bash programming is relatively easy. However, if you have never used Bash, you will be happy to know that it is a simple language built for clarity and simplicity.

Interaction design

Sometimes the hardest thing to figure out when learning to program is what a computer can do for you. Obviously, if a computer can do everything you have to do on its own, then you don't have to touch the computer anymore. But the reality is that humans are important. The key to finding your computer that can help you is to pay attention to the tasks you need to repeat within a week. Computers are especially good at repetitive tasks.

However, in order to tell the computer to do something for you, you must know how to do it. This is what Bash is good at: interactive programming. When you perform an action in a terminal, you are also learning how to write a script.

For example, I used to be responsible for converting a large number of PDF books to low-ink and friendly print versions. One way is to open PDF in the PDF editor, select each of the hundreds of images (page backgrounds and textures count as images), delete them, and save them to the new PDF. It's just a book, so it takes half a day.

My first idea was to learn how to script PDF editors, but after days of research, I couldn't find a script that could write and edit PDF applications (except for very ugly mouse automation tricks). So I turned my attention to finding a way to accomplish the task from the terminal. This led me to several new discoveries, including GhostScript, an open source version of PostScript (the printer language on which PDF is based). By using GhostScript to deal with the task for a few days, I confirmed that this was the solution to my problem.

Writing a basic script to run commands is nothing more than copying the commands and options I used to delete images from PDF and pasting them into a text file. Running this file as a script will probably produce the same result.

Pass parameters to the Bash script

The difference between running commands in a terminal and running commands in a Shell script is that the former is interactive. In the terminal, you can adjust it at any time. For example, if I have just worked on example_1.pdf and are ready to work on the next document to accommodate my command, I only need to change the file name.

Shell scripts are not interactive. In fact, the only reason Shell scripts exist is so that you don't have to participate in person. This is why commands (and the Shell scripts that run them) accept parameters.

In Shell scripts, there are predefined variables that reflect how the script is started. The initial variable is $0, which represents the command to start the script. The next variable is $1, which represents the first "parameter" passed to the Shell script. For example, in the command echo hello, the command echo is $010, the keyword hello is $1, and world is $2.

The interaction in Shell is as follows:

$echo hello worldhello world

In non-interactive Shell scripts, you can do the same thing in a very intuitive way. Enter this text into the text file and save it as hello.sh:

Echo hello world

Execute this script:

$bash hello.shhello world

It's also possible, but it doesn't take advantage of the fact that scripts can accept input. Change the hello.sh to:

Echo $1

Use quotation marks to combine the two parameters to run the script:

$bash hello.sh "hello bash" hello bash

For my PDF slimming project, I really need this non-interactivity, because each PDF takes a few minutes to compress. But by creating a script that accepts my input, I can submit several PDF files to the script at a time. The script processes each file sequentially, which may take half an hour or a little longer, but I can do other tasks in half an hour.

Process control

It is perfectly acceptable to create Bash scripts, which in essence are copies of the exact process that you begin to implement that requires repetition of the task. However, scripts can be made more powerful by controlling the flow of information. A common way to manage the response of scripts to data is:

If/then select structure statement

For loop structure statement

While loop structure statement

Case statement

Computers are not intelligent, but they are good at comparing and analyzing data. If you build some data analysis in the script, the script will become smarter. For example, a basic hello.sh script is displayed with or without content when it is run:

$bash hello.sh foofoo$ bash hello.sh $

It will be easier to use if you provide a help message without receiving input. The following is an if/then statement. If you use Bash in a basic way, you may not know that such a statement exists in Bash. But part of programming is learning the language, and through some research, you'll learn about if/then statements:

If ["$1" = ""]; then echo "syntax: $0 WORD" echo "If you provide more than one word, enclose them in quotes." else echo "$1" fi

The output of running the new version of hello.sh is as follows:

$bash hello.shsyntax: hello.sh WORDIf you provide more than one word, enclose them in quotes.$ bash hello.sh "hello world" hello world works with scripts

Whether you're looking for images to delete from PDF files, managing messy download folders, or creating and providing Kubernetes images, learning to write Bash scripts requires you to use Bash first, and then learn how to change these scripts from just a list of commands to something that responds to input. Usually this is a process of discovery: you are sure to find new Linux commands to perform tasks you never imagined could be performed with text commands, and you will find new features in Bash that adapt your scripts to all the different ways you want them to run.

One way to learn these skills is to read other people's scripts. Learn how people automate rigid commands on their systems. Look at what you are familiar with and look for more information about unfamiliar things.

Another way is to download our introduction to Bash programming ebook. It introduces you to Bash-specific programming concepts, and by learning how to construct, you can start building your own commands. Of course, it's free and licensed under the Creative Commons license, so get it today.

Thank you for reading this article carefully. I hope the article "how to get started with Bash programming" shared by the editor will be helpful to everyone. At the same time, I also hope you will support us and pay attention to the industry information channel. More related knowledge is waiting for you to learn!

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.