Advanced

The [Basics] showed how to access arguments for a command. They are all retrieved as strings which is fine but it we need to say get integers or timestamps the user would have to convert from string to desired type. To ease the burden on users the cli library offers predefined Arg and Args structure to faciliate this The value of the argument can be retrieved using the command.Arg() function. For e.g

package main

import (
    "fmt"
    "log"
    "os"
    "context"

    "github.com/urfave/cli/v3"
)

func main() {
    cmd := &cli.Command{
        Arguments: []cli.Argument{
            &cli.IntArg{
                Name: "someint",
            },
        },
        Action: func(ctx context.Context, cmd *cli.Command) error {
            fmt.Printf("We got %d", cmd.IntArg("someint"))
            return nil
        },
    }

    if err := cmd.Run(context.Background(), os.Args); err != nil {
        log.Fatal(err)
    }
}

Running this program with an argument gives the following output

$ greet 10
We got 10

Instead of using the cmd.XXXArg() function to retrieve the argument value a destination for the argument can be set for e.g

package main

import (
    "fmt"
    "log"
    "os"
    "context"

    "github.com/urfave/cli/v3"
)

func main() {
    var ival int
    cmd := &cli.Command{
        Arguments: []cli.Argument{
            &cli.IntArg{
                Name: "someint",
                Destination: &ival,
            },
        },
        Action: func(ctx context.Context, cmd *cli.Command) error {
            fmt.Printf("We got %d", ival)
            return nil
        },
    }

    if err := cmd.Run(context.Background(), os.Args); err != nil {
        log.Fatal(err)
    }
}

Some of the basic types arguments suported are

• FloatArg
• IntArg
• Int8Arg
• Int16Arg
• Int32Arg
• Int64Arg
• StringArg
• UintArg
• Uint8Arg
• Uint16Arg
• Uint32Arg
• Uint64Arg
• TimestampArg

This is ok for single value arguments. Any number of these single value arguments can be concatenated in the Arguments slice field of Command.

The library also support multi value arguments for e.g

package main

import (
    "fmt"
    "log"
    "os"
    "context"

    "github.com/urfave/cli/v3"
)

func main() {
    cmd := &cli.Command{
        Arguments: []cli.Argument{
            &cli.IntArgs{
                Name: "someint",
                Min: 0,
                Max: -1,
            },
        },
        Action: func(ctx context.Context, cmd *cli.Command) error {
            fmt.Println("We got ", cmd.IntArgs("someint"))
            return nil
        },
    }

    if err := cmd.Run(context.Background(), os.Args); err != nil {
        log.Fatal(err)
    }
}

Some things to note about multi value arguments

1. They have XXXArgs type instead of XXXArg to differentiate them from single value arguments
2. The Max field needs to be defined to a non zero value without which it cannot be parsed
3. Max field value needs to be greater then the Min field value

As with single value args the destination field can be set

package main

import (
    "fmt"
    "log"
    "os"
    "context"

    "github.com/urfave/cli/v3"
)

func main() {
    var ivals []int
    cmd := &cli.Command{
        Arguments: []cli.Argument{
            &cli.IntArgs{
                Name: "someint",
                Min: 0,
                Max: -1,
                Destination: &ivals,
            },
        },
        Action: func(ctx context.Context, cmd *cli.Command) error {
            fmt.Println("We got ", ivals)
            return nil
        },
    }

    if err := cmd.Run(context.Background(), os.Args); err != nil {
        log.Fatal(err)
    }
}

Following multi value arguments are supported

• FloatArgs
• IntArgs
• Int8Args
• Int16Args
• Int32Args
• Int64Args
• StringArgs
• UintArgs
• Uint8Args
• Uint16Args
• Uint32Args
• Uint64Args
• TimestampArgs

It goes without saying that the chain of arguments set in the Arguments slice need to be consistent. Generally a glob argument(max=-1) should be set for the argument at the end of the slice. To glob args we arent interested in we coud add the following to the end of the Arguments slice and retrieve them as a slice

    &StringArgs{
        Max: -1,
    },