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[#]: subject: "How to include options in your Bash shell scripts"
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[#]: via: "https://opensource.com/article/21/8/option-parsing-bash"
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[#]: author: "Seth Kenlon https://opensource.com/users/seth"
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[#]: collector: "lujun9972"
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[#]: translator: "unigeorge"
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[#]: reviewer: " "
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[#]: publisher: " "
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[#]: url: " "
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How to include options in your Bash shell scripts
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======
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Give your shell scripts options.
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![Terminal commands][1]
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Terminal commands usually have [options or switches][2], which you can use to modify how the command does what it does. Options are included in the [POSIX specification][3] for command-line interfaces. It's also a time-honored convention established with the earliest UNIX applications, so it's good to know how to include them in your [Bash scripts][4] when you're creating your own commands.
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As with most languages, there are several ways to solve the problem of parsing options in Bash. To this day, my favorite method remains the one I learned from Patrick Volkerding's Slackware build scripts, which served as my introduction to shell scripting back when I first discovered Linux and dared to venture into the plain text files that shipped with the OS.
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### Option parsing in Bash
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The strategy for parsing options in Bash is to cycle through all arguments passed to your shell script, determine whether they are an option or not, and then shift to the next argument. Repeat this process until no options remain.
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Start with a simple Boolean option (sometimes called a _switch_ or a _flag_):
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```
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#!/bin/bash
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while [ True ]; do
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if [ "$1" = "--alpha" -o "$1" = "-a" ]; then
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ALPHA=1
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shift 1
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else
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break
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fi
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done
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echo $ALPHA
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```
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In this code, I create a `while` loop which serves as an infinite loop until there are no further arguments to process. An `if` statement attempts to match whatever argument is found in the first position (`$1`) to either `--alpha` or `-a`. (These are arbitrary option names with no special significance. In an actual script, you might use `--verbose` and `-v` to trigger verbose output).
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The `shift` keyword causes all arguments to shift by 1, such that an argument in position 2 (`$2`) is moved into position 1 (`$1`). The `else` statement is triggered when there are no further arguments to process, which breaks the `while` loop.
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At the end of the script, the value of `$ALPHA` is printed to the terminal.
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Test the script:
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```
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$ bash ./test.sh --alpha
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1
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$ bash ./test.sh
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$ bash ./test.sh -a
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1
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```
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The option is correctly detected.
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### Detecting arguments in Bash
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There is a problem, though: Extra arguments are ignored.
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```
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$ bash ./test.sh --alpha foo
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1
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$
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```
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To catch arguments that aren't intended as options, you can dump remaining arguments into a [Bash array][5].
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```
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#!/bin/bash
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while [ True ]; do
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if [ "$1" = "--alpha" -o "$1" = "-a" ]; then
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ALPHA=1
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shift 1
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else
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break
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fi
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done
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echo $ALPHA
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ARG=( "${@}" )
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for i in ${ARG[@]}; do
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echo $i
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done
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```
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Test the new version of the script:
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```
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$ bash ./test.sh --alpha foo
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1
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foo
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$ bash ./test.sh foo
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foo
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$ bash ./test.sh --alpha foo bar
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1
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foo
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bar
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```
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### Options with arguments
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Some options require an argument all their own. For instance, you might want to allow the user to set an attribute such as a color or the resolution of a graphic or to point your application to a custom configuration file.
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To implement this in Bash, you can use the `shift` keyword as you do with Boolean switches but shift the arguments by 2 instead of 1.
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```
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#!/bin/bash
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while [ True ]; do
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if [ "$1" = "--alpha" -o "$1" = "-a" ]; then
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ALPHA=1
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shift 1
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elif [ "$1" = "--config" -o "$1" = "-c" ]; then
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CONFIG=$2
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shift 2
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else
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break
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fi
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done
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echo $ALPHA
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echo $CONFIG
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ARG=( "${@}" )
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for i in ${ARG[@]}; do
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echo $i
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done
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```
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In this code, I add an `elif` clause to compare each argument to both `--config` and `-c`. In the event of a match, the value of a variable called `CONFIG` is set to the value of whatever the second argument is (this means that the `--config` option requires an argument). All arguments shift place by 2: 1 to shift `--config` or `-c`, and 1 to move its argument. As usual, the loop repeats until no matching arguments remain.
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Here's a test of the new version of the script:
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```
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$ bash ./test.sh --config my.conf foo bar
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my.conf
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foo
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bar
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$ bash ./test.sh -a --config my.conf baz
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1
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my.conf
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baz
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```
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### Option parsing made easy
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There are other ways to parse options in Bash. You can alternately use a `case` statement or the `getopt` command. Whatever you choose to use, options for your users are important features for any application, and Bash makes it easy.
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--------------------------------------------------------------------------------
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via: https://opensource.com/article/21/8/option-parsing-bash
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作者：[Seth Kenlon][a]
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选题：[lujun9972][b]
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译者：[unigeorge](https://github.com/unigeorge)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://opensource.com/users/seth
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[b]: https://github.com/lujun9972
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[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/terminal-commands_1.png?itok=Va3FdaMB (Terminal commands)
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[2]: https://opensource.com/article/21/8/linux-terminal#options
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[3]: https://opensource.com/article/19/7/what-posix-richard-stallman-explains
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[4]: https://opensource.com/downloads/bash-scripting-ebook
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[5]: https://opensource.com/article/18/5/you-dont-know-bash-intro-bash-arrays
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@ -0,0 +1,172 @@
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[#]: subject: "How to include options in your Bash shell scripts"
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[#]: via: "https://opensource.com/article/21/8/option-parsing-bash"
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[#]: author: "Seth Kenlon https://opensource.com/users/seth"
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[#]: collector: "lujun9972"
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[#]: translator: "unigeorge"
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[#]: reviewer: " "
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[#]: publisher: " "
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[#]: url: " "
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如何在 Bash shell 脚本中解析命令行选项
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======
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把选项交给你的 shell 脚本吧。
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![Terminal commands][1]
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终端命令通常具有 [<ruby>选项<rt>options or switches</rt></ruby>][2] 功能，用户可以使用选项来修改命令的执行方式。关于命令行接口的 [POSIX 规范][3] 中就对选项做出了规范，这也是基于最早的 UNIX 应用程序建立的一个由来已久的约定，因此你在创建自己的命令时，最好知道如何将选项包含进 [Bash 脚本][4] 中。
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与大多数语言一样，有若干种方法可以解决 Bash 中解析选项的问题。但直到今天，我最喜欢的方法仍然是我从 Patrick Volkerding 的 Slackware 构建脚本中学到的方法，当我第一次得知 Linux 并勇于探索操作系统附带的纯文本文件时，它就是我关于 shell 脚本的引路人。
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### Bash 中的选项解析
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在 Bash 中解析选项的策略是循环遍历传递给 shell 脚本的所有参数，确定它们是否为选项，然后转移到下一个参数。重复这个过程，直到没有选项为止。
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```
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#!/bin/bash
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while [ True ]; do
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if [ "$1" = "--alpha" -o "$1" = "-a" ]; then
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ALPHA=1
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shift 1
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else
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break
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fi
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done
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echo $ALPHA
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```
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在这段代码中，我创建了一个 `while` 循环，它会一直进行循环操作，直到处理完所有参数。`if` 语句会试着将在第一个位置（`$1`）中找到的参数与 `--alpha` 或 `-a` 匹配。（此处的待匹配项是任意选项名称，并没有特殊意义。在实际的脚本中，你可以使用 `--verbose` 和 `-v` 来触发详细输出）。
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`shift` 关键字会使所有参数向后移动一位，这样位置 2（`$2`）的参数移动到位置 1（`$1`）。处理完所有参数后会触发 else 语句，进而中断 while 循环。
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在脚本的末尾，`$ALPHA` 的值会输出到终端。
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测试一下这个脚本:
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```
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$ bash ./test.sh --alpha
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1
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$ bash ./test.sh
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$ bash ./test.sh -a
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1
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```
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可以看到，选项被正确地检测到了。
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### 在 Bash 中检测参数
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但上面的脚本还有一个问题：多余的参数被忽略了。
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```
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$ bash ./test.sh --alpha foo
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1
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$
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```
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要想捕获非选项名的参数，可以将剩余的参数转储到 [Bash 数组][5] 中。
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```
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#!/bin/bash
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while [ True ]; do
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if [ "$1" = "--alpha" -o "$1" = "-a" ]; then
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ALPHA=1
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shift 1
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else
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break
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fi
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done
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echo $ALPHA
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ARG=( "${@}" )
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for i in ${ARG[@]}; do
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echo $i
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done
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```
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测试一下新版的脚本：
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```
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$ bash ./test.sh --alpha foo
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1
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foo
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$ bash ./test.sh foo
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foo
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$ bash ./test.sh --alpha foo bar
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1
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foo
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bar
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```
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### 带参选项
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有一些选项需要传入参数。比如，你可能希望允许用户设置诸如颜色或图形分辨率之类的属性，或者将应用程序指向自定义配置文件。
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要在 Bash 中实现这一点，你仍然可以像使用布尔选项一样使用 `shift` 关键字，但参数需要向后移动两位而不是一位。
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```
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#!/bin/bash
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while [ True ]; do
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if [ "$1" = "--alpha" -o "$1" = "-a" ]; then
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ALPHA=1
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shift 1
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elif [ "$1" = "--config" -o "$1" = "-c" ]; then
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CONFIG=$2
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shift 2
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else
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break
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fi
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done
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echo $ALPHA
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echo $CONFIG
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ARG=( "${@}" )
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for i in ${ARG[@]}; do
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echo $i
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done
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```
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在这段代码中，我添加了一个 `elif` 子句来将每个参数与 `--config` 和 `-c` 进行比较。如果匹配，名为 `CONFIG` 的变量的值就设置为下一个参数的值（这就表示 `--config` 选项需要一个参数）。所有参数都后移两位：其中一位是跳过 `--config` 或 `-c`，另一位是跳过其参数。与上节一样，循环重复直到没有匹配的参数。
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下面是新版脚本的测试：
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```
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$ bash ./test.sh --config my.conf foo bar
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my.conf
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foo
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bar
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$ bash ./test.sh -a --config my.conf baz
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1
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my.conf
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baz
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```
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### Bash 让选项解析变得简单
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还有一些其他方法也可以解析 Bash 中的选项。你可以交替使用 `case` 语句或 `getopt` 命令。无论使用什么方法，用户选项都是应用程序的重要功能，而 Bash 让解析选项成为了一件简单的事。
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--------------------------------------------------------------------------------
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via: https://opensource.com/article/21/8/option-parsing-bash
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作者：[Seth Kenlon][a]
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选题：[lujun9972][b]
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译者：[unigeorge](https://github.com/unigeorge)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://opensource.com/users/seth
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[b]: https://github.com/lujun9972
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[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/terminal-commands_1.png?itok=Va3FdaMB (Terminal commands)
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[2]: https://opensource.com/article/21/8/linux-terminal#options
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[3]: https://opensource.com/article/19/7/what-posix-richard-stallman-explains
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[4]: https://opensource.com/downloads/bash-scripting-ebook
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[5]: https://opensource.com/article/18/5/you-dont-know-bash-intro-bash-arrays
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