textctl.go

Documentation: github.com/peterbourgon/ff/v3/ffcli/examples/textctl

     1  package main
     2  
     3  import (
     4  	"context"
     5  	"flag"
     6  	"fmt"
     7  	"os"
     8  
     9  	"github.com/peterbourgon/ff/v3/ffcli"
    10  )
    11  
    12  // textctl is a simple applications in which all commands are built up in func
    13  // main. It demonstrates how to declare minimal commands, how to wire them
    14  // together into a command tree, and one way to allow subcommands access to
    15  // flags set in parent commands.
    16  
    17  func main() {
    18  	var (
    19  		rootFlagSet   = flag.NewFlagSet("textctl", flag.ExitOnError)
    20  		verbose       = rootFlagSet.Bool("v", false, "increase log verbosity")
    21  		repeatFlagSet = flag.NewFlagSet("textctl repeat", flag.ExitOnError)
    22  		n             = repeatFlagSet.Int("n", 3, "how many times to repeat")
    23  	)
    24  
    25  	repeat := &ffcli.Command{
    26  		Name:       "repeat",
    27  		ShortUsage: "textctl repeat [-n times] <arg>",
    28  		ShortHelp:  "Repeatedly print the argument to stdout.",
    29  		FlagSet:    repeatFlagSet,
    30  		Exec: func(_ context.Context, args []string) error {
    31  			if n := len(args); n != 1 {
    32  				return fmt.Errorf("repeat requires exactly 1 argument, but you provided %d", n)
    33  			}
    34  			if *verbose {
    35  				fmt.Fprintf(os.Stderr, "repeat: will generate %dB of output\n", (*n)*len(args[0]))
    36  			}
    37  			for i := 0; i < *n; i++ {
    38  				fmt.Fprintf(os.Stdout, "%s\n", args[0])
    39  			}
    40  			return nil
    41  		},
    42  	}
    43  
    44  	count := &ffcli.Command{
    45  		Name:       "count",
    46  		ShortUsage: "count [<arg> ...]",
    47  		ShortHelp:  "Count the number of bytes in the arguments.",
    48  		Exec: func(_ context.Context, args []string) error {
    49  			if *verbose {
    50  				fmt.Fprintf(os.Stderr, "count: argument count %d\n", len(args))
    51  			}
    52  			var n int
    53  			for _, arg := range args {
    54  				n += len(arg)
    55  			}
    56  			fmt.Fprintf(os.Stdout, "%d\n", n)
    57  			return nil
    58  		},
    59  	}
    60  
    61  	root := &ffcli.Command{
    62  		ShortUsage:  "textctl [flags] <subcommand>",
    63  		FlagSet:     rootFlagSet,
    64  		Subcommands: []*ffcli.Command{repeat, count},
    65  		Exec: func(context.Context, []string) error {
    66  			return flag.ErrHelp
    67  		},
    68  	}
    69  
    70  	if err := root.ParseAndRun(context.Background(), os.Args[1:]); err != nil {
    71  		fmt.Fprintf(os.Stderr, "error: %v\n", err)
    72  		os.Exit(1)
    73  	}
    74  }
    75
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