cmd/epoch: command line to print and parse Unix timestamp

Program epoch print the current time (Unix seconds, milliseconds,
nanoseconds, local time, and UTC time) or the time based on the epoch on
first parameter.
Usage,

	epoch <unix-seconds|unix-milliseconds|unix-nanoseconds>

Without a parameter, it will print the current time.
With single parameter, it will print the time based on that epoch.

1 files changed, 86 insertions, 0 deletions

diff --git a/cmd/epoch/main.go b/cmd/epoch/main.go
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+++ b/cmd/epoch/main.go
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+// Copyright 2021, Shulhan <ms@kilabit.info>. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+/*
+Program epoch print the current time (Unix seconds, milliseconds,
+nanoseconds, local time, and UTC time) or the time based on the epoch on
+first parameter.
+Usage,
+
+	epoch <unix-seconds|unix-milliseconds|unix-nanoseconds>
+
+Without a parameter, it will print the current time.
+With single parameter, it will print the time based on that epoch.
+
+Example,
+
+	$ epoch
+
+	Unix seconds: 1639896843
+	  Unix milli: 1639896843382
+	  Unix micro: 1639896843382879
+	   Unix nano: 1639896843382879358
+	  Local time: 2021-12-19 13:54:03.382879358 +0700 WIB m=+0.000041439
+	    UTC time: 2021-12-19 06:54:03.382879358 +0000 UTC
+
+
+	$ epoch 1639800000
+
+	Unix seconds: 1639800000
+	  Unix milli: 1639800000000
+	  Unix micro: 1639800000000000
+	   Unix nano: 1639800000000000000
+	  Local time: 2021-12-18 11:00:00 +0700 WIB
+	    UTC time: 2021-12-18 04:00:00 +0000 UTC
+*/
+package main
+
+import (
+	"flag"
+	"fmt"
+	"log"
+	"strconv"
+	"time"
+)
+
+func main() {
+	flag.Parse()
+
+	ts := flag.Arg(0)
+
+	if len(ts) == 0 {
+		echo(time.Now())
+		return
+	}
+
+	var t time.Time
+
+	epoch, err := strconv.ParseInt(ts, 10, 64)
+	if err != nil {
+		log.Fatalf("invalid epoch %s: %s", ts, err)
+	}
+
+	switch len(ts) {
+	case 10: // Epoch in seconds.
+		t = time.Unix(epoch, 0)
+	case 13:
+		t = time.UnixMilli(epoch)
+	case 16:
+		t = time.UnixMicro(epoch)
+	}
+
+	echo(t)
+}
+
+func echo(t time.Time) {
+	fmt.Printf(`
+Unix seconds: %d
+  Unix milli: %d
+  Unix micro: %d
+   Unix nano: %d
+  Local time: %s
+    UTC time: %s
+`, t.Unix(), t.UnixMilli(), t.UnixMicro(), t.UnixNano(), t, t.UTC())
+
+}