Merge pull request #18060 from lujun9972/add-MjAyMDA0MTAgR2V0IHN0YXJ0ZWQgd2l0aCBCYXNoIHByb2dyYW1taW5nLm1kCg==

自动选题: 20200410 Get started with Bash programming

sources/tech/20200410 Get started with Bash programming.md

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+[#]: collector: (lujun9972)
+[#]: translator: ( )
+[#]: reviewer: ( )
+[#]: publisher: ( )
+[#]: url: ( )
+[#]: subject: (Get started with Bash programming)
+[#]: via: (https://opensource.com/article/20/4/bash-programming-guide)
+[#]: author: (Seth Kenlon https://opensource.com/users/seth)
+
+Get started with Bash programming
+======
+Learn how to write custom programs in Bash to automate your repetitive
+tasks. Download our new eBook to get started.
+![Command line prompt][1]
+
+One of the original hopes for Unix was that it would empower everyday computer users to fine-tune their computers to match their unique working style. The expectations around computer customization have diminished over the decades, and many users consider their collection of apps and websites to be their "custom environment." One reason for that is that the components of many operating systems are not open, so their source code isn't available to normal users.
+
+But for Linux users, custom programs are within reach because the entire system is based around commands available through the terminal. The terminal isn't just an interface for quick commands or in-depth troubleshooting; it's a scripting environment that can reduce your workload by taking care of mundane tasks for you.
+
+### How to learn programming
+
+If you've never done any programming before, it might help to think of it in terms of two different challenges: one is to understand how code is written, and the other is to understand what code to write. You can learn _syntax_—but you won't get far without knowing what words are available to you in the _language_. In practice, you start learning both concepts all at once because you can't learn syntax without words to arrange, so initially, you write simple tasks using basic commands and basic programming structures. Once you feel comfortable with the basics, you can explore more of the language so you can make your programs do more and more significant things.
+
+In [Bash][2], most of the _words_ you use are Linux commands. The _syntax_ is Bash. If you already use Bash on a frequent basis, then the transition to Bash programming is relatively easy. But if you don't use Bash, you'll be pleased to learn that it's a simple language built for clarity and simplicity.
+
+### Interactive design
+
+Sometimes, the hardest thing to figure out when learning to program is what a computer can do for you. Obviously, if a computer on its own could do everything you do with it, then you wouldn't have to ever touch a computer again. But the reality is that humans are important. The key to finding something your computer can help you with is to take notice of tasks you repeatedly do throughout the week. Computers handle repetition particularly well.
+
+But for you to be able to tell your computer to do something, you must know how to do it. This is an area Bash excels in: interactive programming. As you perform an action in the terminal, you are also learning how to script it.
+
+For instance, I was once tasked with converting a large number of PDF books to versions that would be low-ink and printer-friendly. One way to do this is to open the PDF in a PDF editor, select each one of the hundreds of images—page backgrounds and textures counted as images—delete them, and then save it to a new PDF. Just one book would take half a day this way.
+
+My first thought was to learn how to script a PDF editor, but after days of research, I could not find a PDF editing application that could be scripted (outside of very ugly mouse-automation hacks). So I turned my attention to finding out to accomplish the task from within a terminal. This resulted in several new discoveries, including GhostScript, the open source version of PostScript (the printer language PDF is based on). By using GhostScript for the task for a few days, I confirmed that it was the solution to my problem.
+
+Formulating a basic script to run the command was merely a matter of copying the command and options I used to remove images from a PDF and pasting them into a text file. Running the file as a script would, presumably, produce the same results.
+
+### Passing arguments to a Bash script
+
+The difference between running a command in a terminal and running a command in a shell script is that the former is interactive. In a terminal, you can adjust things as you go. For instance, if I just processed **example_1.pdf** and am ready to process the next document, to adapt my command, I only need to change the filename.
+
+A shell script isn't interactive, though. In fact, the only reason a shell _script_ exists is so that you don't have to attend to it. This is why commands (and the shell scripts that run them) accept arguments.
+
+In a shell script, there are a few predefined variables that reflect how a script starts. The initial variable is **$0**, and it represents the command issued to start the script. The next variable is **$1**, which represents the first "argument" passed to the shell script. For example, in the command **echo hello**, the command **echo** is **$0,** and the word **hello** is **$1**. In the command **echo hello world**, the command **echo** is **$0**, **hello** is **$1**, and **world** is **$2**.
+
+In an interactive shell:
+
+
+```
+$ echo hello world
+hello world
+```
+
+In a non-interactive shell script, you _could_ do the same thing in a very literal way. Type this text into a text file and save it as **hello.sh**:
+
+
+```
+`echo hello world`
+```
+
+Now run the script:
+
+
+```
+$ bash hello.sh
+hello world
+```
+
+That works, but it doesn't take advantage of the fact that a script can take input. Change **hello.sh** to this:
+
+
+```
+`echo $1`
+```
+
+Run the script with two arguments grouped together as one with quotation marks:
+
+
+```
+$ bash hello.sh "hello bash"
+hello bash
+```
+
+For my PDF reduction project, I had a real need for this kind of non-interactivity, because each PDF took several minutes to condense. But by creating a script that accepted input from me, I could feed the script several PDF files all at once. The script processed each one sequentially, which could take half an hour or more, but it was a half-hour I could use for other tasks.
+
+### Flow control
+
+It's perfectly acceptable to create Bash scripts that are, essentially, transcripts of the exact process you took to achieve the task you need to be repeated. However, scripts can be made more powerful by controlling how information flows through them. Common methods of managing a script's response to data are:
+
+  * if/then
+  * for loops
+  * while loops
+  * case statements
+
+
+
+Computers aren't intelligent, but they are good at comparing and parsing data. Scripts can feel a lot more intelligent if you build some data analysis into them. For example, the basic **hello.sh** script runs whether or not there's anything to echo:
+
+
+```
+$ bash hello.sh foo
+foo
+$ bash hello.sh
+
+$
+```
+
+It would be more user-friendly if it provided a help message when it receives no input. That's an if/then statement, and if you're using Bash in a basic way, you probably wouldn't know that such a statement existed in Bash. But part of programming is learning the language, and with a little research you'd 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 "$1"
+fi
+```
+
+Running this new version of **hello.sh** results in:
+
+
+```
+$ bash hello.sh
+syntax: hello.sh WORD
+If you provide more than one word, enclose them in quotes.
+$ bash hello.sh "hello world"
+hello world
+```
+
+### Working your way through a script
+
+Whether you're looking for something to remove images from PDF files, or something to manage your cluttered Downloads folder, or something to create and provision Kubernetes images, learning to script Bash is a matter of using Bash and then learning ways to take those scripts from just a list of commands to something that responds to input. It's usually a process of discovery: you're bound to find new Linux commands that perform tasks you never imagined could be performed with text commands, and you'll find new functions of Bash to make your scripts adaptable to all the different ways you want them to run.
+
+One way to learn these tricks is to read other people's scripts. Get a feel for how people are automating rote commands on their systems. See what looks familiar to you, and look for more information about the things that are unfamiliar.
+
+Another way is to download our [introduction to programming with Bash][3] eBook. It introduces you to programming concepts specific to Bash, and with the constructs you learn, you can start to build your own commands. And of course, it's free to download and licensed under a [Creative Commons][4] license, so grab your copy today.
+
+### [Download our introduction to programming with Bash eBook!][3]
+
+--------------------------------------------------------------------------------
+
+via: https://opensource.com/article/20/4/bash-programming-guide
+
+作者：[Seth Kenlon][a]
+选题：[lujun9972][b]
+译者：[译者ID](https://github.com/译者ID)
+校对：[校对者ID](https://github.com/校对者ID)
+
+本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
+
+[a]: https://opensource.com/users/seth
+[b]: https://github.com/lujun9972
+[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/command_line_prompt.png?itok=wbGiJ_yg (Command line prompt)
+[2]: https://opensource.com/resources/what-bash
+[3]: https://opensource.com/downloads/bash-programming-guide
+[4]: https://opensource.com/article/20/1/what-creative-commons

sources/tech/20200410 How Kubernetes saved my desktop application.md

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+[#]: collector: (lujun9972)
+[#]: translator: ( )
+[#]: reviewer: ( )
+[#]: publisher: ( )
+[#]: url: ( )
+[#]: subject: (How Kubernetes saved my desktop application)
+[#]: via: (https://opensource.com/article/20/4/kubernetes-desktop-application)
+[#]: author: (Chris Hermansen https://opensource.com/users/clhermansen)
+
+How Kubernetes saved my desktop application
+======
+Keep this fix in mind if you have a broken Java desktop application but
+aren't a crypto expert.
+![Puzzle pieces coming together to form a computer screen][1]
+
+Recently, fellow Opensource.com scribe James Farrell wrote a wonderful article entitled _[How Ansible brought peace to my home][2]_. In addition to the great article, I really liked the title, one of those unexpected phrases that I’m sure brought a smile to many faces.
+
+I recently had a weird but positive experience of my own that begs a similar sort of unexpected label. I’ve been grappling with a difficult problem that arose when upgrading some server and networking infrastructure that broke a Java application I’ve been supporting since the early 2000s. Strangely enough, I found the solution in what appears to be a very informative and excellent article on Kubernetes, of all things.
+
+Without further ado, here is my problem:
+
+![][3]
+
+I’m guessing that most readers will look at that message and think things like, "I hope there’s more info in the log file," or "I’m really glad I’ve never received a message like that."
+
+Unfortunately, there isn’t a lot of info in the log file, just the same message, in fact. In an effort to debug this, I did three things:
+
+  1. I searched online for the message. Interestingly, or perhaps ominously, there were only 200 or so hits on this string, [one of which suggested][4] [turn][4][ing][4] [on more debugging output][4], which involved adding the setting
+
+
+```
+**-Djavax.net.debug=ssl:handshake:verbose**[/code] to the **java** command running the application.
+
+  2. I tried that suggestion, which resulted in a lot of output (good), most of which only vaguely made sense to me as I’m no kind of expert in the underlying bits of stuff like SSL. But one thing I did notice is that there was no information regarding a response from the server in the midst of all of that output;
+
+  3. So I searched some more.
+
+
+
+
+Another interesting part of this problem is that the code ran fine when executed by the Java command bundled in the OpenJDK, but failed with this error when using a customized runtime [created from the same OpenJDK in this way][5]. So the relatively modest number of apparently similar problems turned up from search #1 above were actually not all that relevant since they all seemed to be dealing mostly with bad SSL certificates on the server in conjunction with the PostgreSQL JDBC’s ability to check the server’s credentials.
+
+I should also mention that it took me quite some time to realize that the problem was introduced by using the custom Java runtime, as I managed to check many other possibilities along the way (and indeed, I did fix a few minor bugs while I was at it). My efforts included things like getting the latest OpenJDK, checking and re-checking all the URLs in case one had a typo, and so forth.
+
+As often happens, after putting the problem aside for a few hours, an idea occurred to me—perhaps I was missing some module in the customized Java runtime. While I didn’t receive any errors directly suggesting that problem, the observable fact that the standard OpenJDK environment worked while the custom one failed seemed to hint at that possibility. I took a quick look in the **jmods/** folder in the OpenJDK installation, but there are some 70 modules there and nothing jumped out at me.
+
+But again, what seemed odd was, with debugging turned on (see #1 above), there was no indication of what the server would accept, just what the client mostly couldn’t offer, many lines like this:
+```
+`Ignoring unavailable cipher suite: TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA`
+```
+So I was at least thinking by this time that maybe what was missing was the module that offered those kinds of cipher suites. So I started searching with strings like "jdbc crypto," and in the midst of that, the most unlikely article showed up: [Optimizing Kubernetes Services—Part 2: Spring Web][6], written by [Juan Medina][7]. Midway down the article, I spotted the following:
+
+![][8]
+
+Huh! Imagine that, his script is creating a custom Java runtime, just like mine. But he says he needs to add in manually the module **jdk.crypto.ec** in order t