From b79019217f4f74d8d328d462fdf3faa48cfc3a7e Mon Sep 17 00:00:00 2001 From: DarkSun Date: Wed, 9 Dec 2020 05:02:47 +0800 Subject: [PATCH] =?UTF-8?q?=E9=80=89=E9=A2=98[tech]:=2020201208=20Learn=20?= =?UTF-8?q?Bash=20by=20writing=20an=20interactive=20game?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit sources/tech/20201208 Learn Bash by writing an interactive game.md --- ...arn Bash by writing an interactive game.md | 126 ++++++++++++++++++ 1 file changed, 126 insertions(+) create mode 100644 sources/tech/20201208 Learn Bash by writing an interactive game.md diff --git a/sources/tech/20201208 Learn Bash by writing an interactive game.md b/sources/tech/20201208 Learn Bash by writing an interactive game.md new file mode 100644 index 0000000000..6b8cdfcd05 --- /dev/null +++ b/sources/tech/20201208 Learn Bash by writing an interactive game.md @@ -0,0 +1,126 @@ +[#]: 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