package main import ( "bufio" "flag" "fmt" "io" "os" "time" ) var ( format = "2006-01-02 15:04" // Format that will be used for times. tz = "Local" // String descriptor for timezone. fromLoc *time.Location // Go time.Location for the named timezone. toLoc *time.Location // Go time.Location for output timezone. ) func usage(w io.Writer) { fmt.Fprintf(w, `Usage: utc [-f format] [-u] [-h] [-z zone] [time(s)...] utc converts times to UTC. If no arguments are provided, prints the current time in UTC. Flags: -f format Go timezone format. See the Go documentation (e.g. https://golang.org/pkg/time/#pkg-constants) for an explanation of this format. Default value: %s -h Print this help message. -u Timestamps are in UTC format and should be converted to the timezone specified by the -z argument (which defaults to '%s'). Note that this isn't particularly useful with no arguments. -z zone Text form of the time zone; this can be in short time zone abbreviation (e.g. MST) or a location (e.g. America/Los_Angeles). This has no effect when printing the current time. Default value: %s Examples (note that the examples are done in the America/Los_Angeles / PST8PDT time zone): + Getting the current time in UTC: $ utc 2016-06-14 14:30 = 2016-06-14 21:30 + Converting a local timestamp to UTC: $ utc '2016-06-14 21:30' 2016-06-14 21:30 = 2016-06-15 04:30 + Converting a local EST timestamp to UTC (on a machine set to PST8PDT): $ utc -z EST '2016-06-14 21:30' 2016-06-14 21:30 = 2016-06-15 02:30 + Converting timestamps in the form '14-06-2016 3:04PM': $ utc -f '02-01-2006 3:04PM' '14-06-2016 9:30PM' 14-06-2016 9:30PM = 15-06-2016 4:30AM + Converting timestamps from standard input: $ printf "2016-06-14 14:42\n2016-06-13 11:01" | utc - 2016-06-14 14:42 = 2016-06-14 21:42 2016-06-13 11:01 = 2016-06-13 18:01 + Converting a UTC timestamp to the local time zone: $ utc -u '2016-06-14 21:30' 2016-06-14 21:30 = 2016-06-14 14:30 + Converting a UTC timestamp to EST (on a machine set to PST8PDT): $ utc -u -z EST '2016-06-14 21:30' 2016-06-14 21:30 = 2016-06-14 16:30 `, format, tz, tz) } func init() { var help bool var utc bool flag.Usage = func() { usage(os.Stderr) } flag.StringVar(&format, "f", format, "time format") flag.BoolVar(&help, "h", false, "print usage information") flag.BoolVar(&utc, "u", false, "timestamps are in UTC format") flag.StringVar(&tz, "z", tz, "time zone to convert from; if blank, the local timezone is used") flag.Parse() if help { usage(os.Stdout) os.Exit(0) } if utc { var err error toLoc, err = time.LoadLocation(tz) if err != nil { fmt.Fprintf(os.Stderr, "Malformed timezone %s: %s\n", tz, err) os.Exit(1) } fromLoc = time.UTC } else { var err error fromLoc, err = time.LoadLocation(tz) if err != nil { fmt.Fprintf(os.Stderr, "Malformed timezone %s: %s\n", tz, err) os.Exit(1) } toLoc = time.UTC } } func showTime(t time.Time) { fmt.Printf("%s = %s\n", t.Format(format), t.In(toLoc).Format(format)) } func dumpTimes(times []string) bool { var errored bool for _, t := range times { u, err := time.ParseInLocation(format, t, fromLoc) if err != nil { errored = true fmt.Fprintf(os.Stderr, "Malformed time %s: %s\n", t, err) continue } showTime(u) } return errored } func main() { var times []string n := flag.NArg() switch n { case 0: showTime(time.Now()) os.Exit(0) case 1: if flag.Arg(0) == "-" { s := bufio.NewScanner(os.Stdin) for s.Scan() { times = append(times, s.Text()) } } else { times = flag.Args() } default: times = flag.Args() } if dumpTimes(times) { os.Exit(1) } }