Command-Line Flags {.en}

命令行标志 {.zh}

::: {.en} Command-line flags are a common way to specify options for command-line programs. For example, in wc -l the -l is a command-line flag. :::

::: {.zh}

[Command-line flags]（http://en.wikipedia.org/wiki/Command-line_interface#Command-line_option）是指定命令行程序选项的常用方法。例如，在`wc -l中，-l`是acommand-line标志。

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package main

::: {.en} Go provides a flag package supporting basic command-line flag parsing. We’ll use this package to implement our example command-line program. :::

::: {.zh}

Go提供了一个支持basiccommand-line标志解析的flag包。我们将使用此包来实现我们的示例命令行程序。

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import "flag"
import "fmt"
func main() {

::: {.en} Basic flag declarations are available for string, integer, and boolean options. Here we declare a string flag word with a default value "foo" and a short description. This flag.String function returns a string pointer (not a string value); we’ll see how to use this pointer below. :::

::: {.zh}

基本标志声明可用于字符串，整数和布尔选项。这里我们声明astring标志word，默认值为“foo”和简短描述。这个flag.String函数返回一个字符串指针（不是字符串值）;我们将看到如何在下面使用这个指针。

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    wordPtr := flag.String("word", "foo", "a string")

::: {.en} This declares numb and fork flags, using a similar approach to the word flag. :::

::: {.zh}

这声明了numb和fork标志，使用与word标志类似的方法。

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    numbPtr := flag.Int("numb", 42, "an int")
    boolPtr := flag.Bool("fork", false, "a bool")

::: {.en} It’s also possible to declare an option that uses an existing var declared elsewhere in the program. Note that we need to pass in a pointer to the flag declaration function. :::

::: {.zh}

也可以声明一个使用在程序中其他地方声明的现有var的选项。注意我们需要传入一个指向flagdeclaration函数的指针。

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    var svar string
    flag.StringVar(&svar, "svar", "bar", "a string var")

::: {.en} Once all flags are declared, call flag.Parse() to execute the command-line parsing. :::

::: {.zh}

声明所有标志后，调用flag.Parse（）来执行命令行解析。

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    flag.Parse()

::: {.en} Here we’ll just dump out the parsed options and any trailing positional arguments. Note that we need to dereference the pointers with e.g. *wordPtr to get the actual option values. :::

::: {.zh}

在这里，我们只会转出已解析的选项和任何尾随位置参数。请注意，我们需要取消引用指针，例如* wordPtr获取实际选项值。

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    fmt.Println("word:", *wordPtr)
    fmt.Println("numb:", *numbPtr)
    fmt.Println("fork:", *boolPtr)
    fmt.Println("svar:", svar)
    fmt.Println("tail:", flag.Args())
}

::: {.en} To experiment with the command-line flags program it’s best to first compile it and then run the resulting binary directly. :::

::: {.zh}

要试验命令行标志程序，首先要编译它然后直接运行结果二进制文件。

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$ go build command-line-flags.go

::: {.en} Try out the built program by first giving it values for all flags. :::

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通过首先给它值forall标志来尝试构建的程序。

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$ ./command-line-flags -word=opt -numb=7 -fork -svar=flag
word: opt
numb: 7
fork: true
svar: flag
tail: []

::: {.en} Note that if you omit flags they automatically take their default values. :::

::: {.zh}

请注意，如果省略标记，它们会自动获取默认值。

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$ ./command-line-flags -word=opt
word: opt
numb: 42
fork: false
svar: bar
tail: []

::: {.en} Trailing positional arguments can be provided after any flags. :::

::: {.zh}

可以在后面的标志中提供尾随位置参数。

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$ ./command-line-flags -word=opt a1 a2 a3
word: opt
...
tail: [a1 a2 a3]

::: {.en} Note that the flag package requires all flags to appear before positional arguments (otherwise the flags will be interpreted as positional arguments). :::

::: {.zh}

请注意，flag包需要在位置参数之前出现所有标志（否则标志将被解释为位置参数）。

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$ ./command-line-flags -word=opt a1 a2 a3 -numb=7
word: opt
numb: 42
fork: false
svar: bar
tail: [a1 a2 a3 -numb=7]

::: {.en} Use -h or --help flags to get automatically generated help text for the command-line program. :::

::: {.zh}

使用-h或--help标志来获取命令行程序的自动生成的帮助文本。

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$ ./command-line-flags -h
Usage of ./command-line-flags:
  -fork=false: a bool
  -numb=42: an int
  -svar="bar": a string var
  -word="foo": a string

::: {.en} If you provide a flag that wasn’t specified to the flag package, the program will print an error message and show the help text again. :::

::: {.zh}

如果您提供未指定给flag包的标志，程序将打印错误消息并再次显示帮助文本。

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$ ./command-line-flags -wat
flag provided but not defined: -wat
Usage of ./command-line-flags:
...

::: {.en} Next we’ll look at environment variables, another common way to parameterize programs. :::

::: {.zh}

接下来我们将看一下环境变量，这是另一个参数化程序的常用方法。

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