prefixes merge utility

package main

import (
    "bufio"
    "flag"
    "fmt"
    "net/netip"
    "os"

    "go4.org/netipx"
)

var input = flag.String("f", "", "Specify input file")

func main() {
    flag.Parse()

    var err error
    f := os.Stdin
    if *input != "" {
        if f, err = os.Open(*input); err != nil {
            panic(err)
        }
        defer f.Close()
    }

    scanner := bufio.NewScanner(f)
    scanner.Split(bufio.ScanLines)
    builder := &netipx.IPSetBuilder{}

    for i := 0; scanner.Scan(); i++ {
        str := scanner.Text()
        prefix, err := netip.ParsePrefix(str)
        if err != nil {
            fmt.Printf("unable to parse line %d: %s", i, str)
            return
        }

        builder.AddPrefix(prefix)
    }

    if err := scanner.Err(); err != nil {
        panic(err)
    }

    set, err := builder.IPSet()
    if err != nil {
        panic(err)
    }

    for _, p := range set.Prefixes() {
        fmt.Println(p)
    }
}