Go实例: Command-Line Flags

Ianthe ·

更新时间:2024-11-10

· 956 次阅读

package main
import (
    "flag"
    "fmt"
)
func main() {
    wordPtr := flag.String("word", "foo", "a string")
    numbPtr := flag.Int("numb", 42, "an int")
    forkPtr := flag.Bool("fork", false, "a bool")
    var svar string
    flag.StringVar(&svar, "svar", "bar", "a string var")
    flag.Parse()
    fmt.Println("word:", *wordPtr)
    fmt.Println("numb:", *numbPtr)
    fmt.Println("fork:", *forkPtr)
    fmt.Println("svar:", svar)
    fmt.Println("tail:", flag.Args())
}

$ go build command-line-flags.go
Try out the built program by first giving it values for all flags.
$ ./command-line-flags -word=opt -numb=7 -fork -svar=flag
word: opt
numb: 7
fork: true
svar: flag
tail: []
Note that if you omit flags they automatically take their default values.
$ ./command-line-flags -word=opt
word: opt
numb: 42
fork: false
svar: bar
tail: []
Trailing positional arguments can be provided after any flags.
$ ./command-line-flags -word=opt a1 a2 a3
word: opt
...
tail: [a1 a2 a3]
Note that the flag package requires all flags to appear before positional arguments (otherwise the flags will be interpreted as positional arguments).
$ ./command-line-flags -word=opt a1 a2 a3 -numb=7
word: opt
numb: 42
fork: false
svar: bar
tail: [a1 a2 a3 -numb=7]
Use -h or --help flags to get automatically generated help text for the command-line program.
$ ./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
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.
$ ./command-line-flags -wat
flag provided but not defined: -wat
Usage of ./command-line-flags:
...

GO实例 flags GO line

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