Merge pull request #20386 from lujun9972/add-MjAyMDEyMDggTGVhcm4gQmFzaCBieSB3cml0aW5nIGFuIGludGVyYWN0aXZlIGdhbWUubWQK

自动选题[tech]: 20201208 Learn Bash by writing an interactive game

sources/tech/20201208 Learn Bash by writing an interactive game.md

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+[#]: collector: (lujun9972)
+[#]: translator: ( )
+[#]: reviewer: ( )
+[#]: publisher: ( )
+[#]: url: ( )
+[#]: subject: (Learn Bash by writing an interactive game)
+[#]: via: (https://opensource.com/article/20/12/learn-bash)
+[#]: author: (Jim Hall https://opensource.com/users/jim-hall)
+
+Learn Bash by writing an interactive game
+======
+Programming a simple game is a great way to practice a new language and
+compare it against others you know.
+![bash logo on green background][1]
+
+Learning a new programming language can be fun. Whenever I try to learn a new one, I focus on defining variables, writing a statement, and evaluating expressions. Once I have a general understanding of those concepts, I can usually figure out the rest on my own. Most programming languages have some similarities, so once you know one programming language, learning the next one is a matter of figuring out the unique details and recognizing the differences in it.
+
+To help me practice a new programming language, I like to write a few test programs. One sample program I often write is a simple "guess the number" program, where the computer picks a number between one and 100 and asks me to guess the number. The program loops until I guess correctly.
+
+The "guess the number" program exercises several concepts in programming languages: how to assign values to variables, how to write statements, and how to perform conditional evaluation and loops. It's a great practical experiment for learning a new programming language.
+
+### Guess the number in Bash
+
+[Bash][2] is the standard shell for most Linux systems. Aside from providing a rich command-line user interface, Bash also supports a complete programming language in the form of _scripts_.
+
+If you're not familiar with Bash, I recommend these introductions:
+
+  * [What is Bash?][3]
+  * [Get started with Bash programming][4]
+  * [Get started with Bash scripting for sysadmins][5]
+  * [How to write functions in Bash][6]
+  * [Read more about Bash][7]
+
+
+
+You can explore Bash by writing a version of the "guess the number" game. Here is my implementation:
+
+
+```
+#!/bin/bash
+
+number=$(( $RANDOM % 100 + 1 ))
+
+echo "Guess a number between 1 and 100"
+
+guess=0
+
+while [ "0$guess" -ne $number ] ; do
+        read guess
+        [ "0$guess" -lt $number ] && echo "Too low"
+        [ "0$guess" -gt $number ] && echo "Too high"
+done
+
+echo "That's right!"
+exit 0
+```
+
+### Breaking down the script
+
+The first line in the script, `#!/bin/bash` tells Linux to run this script using the Bash shell. Every script starts with the `#!` character pair, which indicates this is a shell script. What immediately follows `#!` is the shell to run. In this case, `/bin/bash` is the Bash shell.
+
+To assign a value to a variable, list the variable's name followed by the `=` sign. For example, the statement `guess=0` assigns a zero value to the `guess` variable.
+
+You can also prompt the user to enter a value using the `read` statement. If you write `read guess`, Bash waits for the user to enter some text then stores that value in the `guess` variable.
+
+To reference the value of a variable, use `$` before the variable name. So, having stored a value in the `guess` variable, you can retrieve it using `$guess`.
+
+You can use whatever names you like for variables, but Bash reserves a few special variable names for itself. One special variable is `RANDOM`, which generates a very large random number every time you reference it.
+
+If you want to perform an operation at the same time you store a value, you need to enclose the statement in special brackets. This tells Bash to execute that statement first, and the `=` stores the resulting value in the variable. To evaluate a mathematical expression, use `$(( ))` around your statement. The double parentheses indicate an _arithmetic expression_. In my example, `number=$(( $RANDOM % 100 + 1 ))` evaluates the expression `$RANDOM % 100 + 1` and then stores the value in the `number` variable.
+
+Standard arithmetic operators such as `+` (plus), `-` (minus), `*` (multiply), `/` (divide), and `%` (modulo) apply.
+
+That means the statement `number=$(( $RANDOM % 100 + 1 ))` generates a random number between one and 100. The modulo operator (`%`) returns the _remainder_ after dividing two numbers. In this case, Bash divides a random number by 100, leaving a remainder in the range zero to 99. By adding one to that value, you get a random number between one and 100.
+
+Bash supports _conditional expressions_ and _flow control_ like loops. In the "guess the number" game, Bash continues looping as long as the value in `guess` is not equal to `number`. If the guess is less than the random number, Bash prints "Too low," and if the guess is greater than the number, Bash prints "Too high."
+
+### How it works
+
+Now that you've written your Bash script, you can run it to play the "guess the number" game. Continue guessing until you find the correct number:
+
+
+```
+Guess a number between 1 and 100
+50
+Too high
+30
+Too high
+20
+Too high
+10
+Too low
+15
+Too high
+13
+Too low
+14
+That's right!
+```
+
+Every time you run the script, Bash will pick a different random number.
+
+This "guess the number" game is a great introductory program when learning a new programming language because it exercises several common programming concepts in a pretty straightforward way. By implementing this simple game in different programming languages, you can demonstrate some core concepts and compare details in each language.
+
+Do you have a favorite programming language? How would you write the "guess the number" game in it? Follow this article series to see examples of other programming languages that might interest you.
+
+--------------------------------------------------------------------------------
+
+via: https://opensource.com/article/20/12/learn-bash
+
+作者：[Jim Hall][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/jim-hall
+[b]: https://github.com/lujun9972
+[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/bash_command_line.png?itok=k4z94W2U (bash logo on green background)
+[2]: https://en.wikipedia.org/wiki/Bash_(Unix_shell)
+[3]: https://opensource.com/resources/what-bash
+[4]: https://opensource.com/article/20/4/bash-programming-guide
+[5]: https://opensource.com/article/20/4/bash-sysadmins-ebook
+[6]: https://opensource.com/article/20/6/bash-functions
+[7]: https://opensource.com/tags/bash