Improve cli help

main.go

@@ -13,14 +13,34 @@ import (
 )
 
 func main() {
+ flag.Usage = func() {
+ out := flag.CommandLine.Output()
+ fmt.Fprintln(out, "Usage: jaggr [OPTIONS] FIELD_DEF [FIELD_DEF...]:")
+ fmt.Fprintln(out, "")
+ fmt.Fprintln(out, "OPTIONS:")
+ flag.PrintDefaults()
+ fmt.Fprintln(out, "")
+ fmt.Fprintln(out, "FIELD_DEF: <aggr>[,<aggr>...]:path[=alias]")
+ fmt.Fprintln(out, " aggr:")
+ fmt.Fprintln(out, " - min, max, mean: Computes the min, max, mean of the field's values during the sample interval.")
+ fmt.Fprintln(out, " - median, p#: The p1 to p99 compute the percentile of the field's values during the sample interval.")
+ fmt.Fprintln(out, " - sum: Sum all values for the field.")
+ fmt.Fprintln(out, " - [bucket1,bucketN]hist: Count number of values between bucket and bucket+1.")
+ fmt.Fprintln(out, " - [bucket1,bucketN]cat: Count number of values equal to the define buckets (can be non-number values). The special `*` matches values that fit in none of the defined buckets.")
+ fmt.Fprintln(out, " path:")
+ fmt.Fprintln(out, " JSON field path (eg: field.sub-field).")
+ fmt.Fprintln(out, " alias:")
+ fmt.Fprintln(out, " Optional name to use instead of the field path on the output.")
+ }
+ interval := flag.Duration("interval", time.Second, "Sampling interval")
  flag.Parse()
  fields, err := aggr.NewFields(flag.Args())
  if err != nil {
  fatal("invalid argument: ", err)
  }
 
  go func() {
- t := time.NewTicker(time.Second)
+ t := time.NewTicker(*interval)
  for range t.C {
  b, err := json.Marshal(fields.Aggr())
  if err != nil {