Basic numfmt butonly for converting to si.

numfmt/.gitignore

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+numfmt
+numfmt.exe

numfmt/Makefile

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+
+
+build:
+	go build .

numfmt/go.mod

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+module lcthw.dev/go/go-coreutils/numfmt
+
+go 1.25.3

numfmt/main.go

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+package main
+
+import (
+    "fmt"
+    "flag"
+    "strconv"
+    "log"
+    "math"
+    "bufio"
+    "os"
+)
+
+type Opts struct {
+    From string
+    To string
+}
+
+func parse_opts() (Opts, []string) {
+    var opts Opts
+
+    flag.StringVar(&opts.From, "from", "", "Convert from")
+    flag.StringVar(&opts.To, "to", "", "Convert to")
+    flag.Parse()
+
+    return opts, flag.Args()
+}
+
+func to_si(num string) string {
+    number, err := strconv.ParseFloat(num, 64)
+    if err != nil { log.Fatal("that's not a number") }
+    mag := math.Floor(math.Log10(number))
+
+    switch {
+    case mag < 3:
+        return num
+    case mag == 3:
+        // need to separate k from hundres
+        as_k := math.Floor(float64(number) / 1000.0)
+        mod := math.Ceil(float64(int(number) % 1000))
+        return fmt.Sprintf("%d.%dk", int(as_k), int(mod))
+    case mag > 3 && mag < 6: 
+        as_m := math.Ceil(float64(number) / 1000.0)
+        return fmt.Sprintf("%dk", int(as_m))
+    case mag == 6:
+        // need to separate mil from k
+        as_m := math.Floor(float64(number) / 1000000.0)
+        mod := math.Ceil(float64(int(number) % 1000000) / 1000.0)
+        return fmt.Sprintf("%d.%dM", int(as_m), int(mod))
+    case mag > 6 && mag <= 9:
+        as_m := math.Ceil(float64(number) / 1000000.0)
+        return fmt.Sprintf("%dM", int(as_m))
+    default:
+        return fmt.Sprintf("%sbesos", num)
+    }
+}
+
+func main() {
+    opts, nums := parse_opts()
+
+    if opts.From != "" {
+        log.Fatal("you should implement this")
+    }
+
+    if len(nums) == 0 {
+        scanner := bufio.NewScanner(os.Stdin)
+        for scanner.Scan() {
+            num := scanner.Text()
+            fmt.Println(to_si(num))
+        }
+    } else {
+        for _, num := range nums {
+            fmt.Println(to_si(num))
+        }
+    }
+}