242 lines
6.5 KiB
Go
242 lines
6.5 KiB
Go
package main
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import (
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"bufio"
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"flag"
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"fmt"
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"io"
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"os"
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"time"
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)
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var (
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format = "2006-01-02 15:04" // Format that will be used for times.
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outFormat = format + " MST" // Output format.
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tz = "Local" // String descriptor for timezone.
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fromLoc *time.Location = time.Local // Go time.Location for the named timezone.
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toLoc *time.Location = time.UTC // Go time.Location for output timezone.
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)
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func usage(w io.Writer) {
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fmt.Fprintf(w, `Usage: utc [-f format] [-h] [-o format] [-q] [-u] [-z zone] [time(s)...]
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utc converts times to UTC. If no arguments are provided, prints the
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current time in UTC. If the only argument provided is "-", utc reads
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newline-separated timestamps from standard input. If the argument is
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"help", it will print an extended help message with examples. If both
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the input and output timezones are the same (e.g., the local time zone
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is UTC), a warning message will be printed on standard error. This can
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be suppressed with the -q option.
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Flags:
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-f format Go timestamp format for input times. See the Go docs
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(e.g. https://golang.org/pkg/time/#pkg-constants)
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for an explanation of this format.
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Default value: %s
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-h Print this help message.
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-o format Go timestamp format for outputting times. It uses
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the same format as the '-f' argument.
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Default value: %s
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-q Suppress the timezone check warning message.
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-u Timestamps are in UTC format and should be converted
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to the timezone specified by the -z argument (which
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defaults to '%s'). Note that this isn't particularly
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useful with no arguments.
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-z zone Text form of the time zone; this can be in short
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time zone abbreviation (e.g. MST) or a location
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(e.g. America/Los_Angeles). This has no effect when
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printing the current time.
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Default value: %s
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`, format, outFormat, tz, tz)
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}
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func usageExamples() {
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usage(os.Stdout)
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fmt.Println(`
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Examples (note that the examples are done in the America/Los_Angeles /
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PST8PDT time zone):
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+ Getting the current time in UTC:
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$ utc
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2016-06-14 14:30 PDT = 2016-06-14 21:30 UTC
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+ Converting a local timestamp to UTC:
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$ utc '2016-06-14 21:30'
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2016-06-14 21:30 PDT = 2016-06-15 04:30 UTC
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+ Converting a local EST timestamp to UTC (on a machine set to
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PST8PDT):
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$ utc -z EST '2016-06-14 21:30'
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2016-06-14 21:30 EST = 2016-06-15 02:30 UTC
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+ Converting timestamps in the form '14-06-2016 3:04PM':
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$ utc -f '02-01-2006 3:04PM' '14-06-2016 9:30PM'
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2016-06-14 21:30 PDT = 2016-06-15 04:30 UTC
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+ Converting timestamps from standard input:
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$ printf "2016-06-14 14:42\n2016-06-13 11:01" | utc -
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2016-06-14 14:42 PDT = 2016-06-14 21:42 UTC
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2016-06-13 11:01 PDT = 2016-06-13 18:01 UTC
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+ Converting a UTC timestamp to the local time zone:
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$ utc -u '2016-06-14 21:30'
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2016-06-14 21:30 UTC = 2016-06-14 14:30 PDT
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+ Converting a UTC timestamp to EST (on a machine set to
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PST8PDT):
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$ utc -u -z EST '2016-06-14 21:30'
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2016-06-14 21:30 UTC = 2016-06-14 16:30 EST
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+ Using a different output format:
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$ utc -o '2006-01-02T15:03:04-0700' '2016-06-14 21:30'
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2016-06-14T21:09:30-0700 = 2016-06-15T04:04:30+0000
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+ Example of the warning message when running utc on a machine
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where the local time zone is UTC:
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$ utc
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==================================================================
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Note: both input and output timezone offsets are the same --- this
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program may not do what you expect it to.
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(Converting from UTC (offset +0000) to UTC (offset +0000).)
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==================================================================
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2016-06-14 23:44 = 2016-06-14 23:44
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+ Example of the warning message when running utc on a machine
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where the local time zone is GMT:
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$ utc
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==================================================================
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Note: both input and output timezone offsets are the same --- this
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program may not do what you expect it to.
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(Converting from GMT (offset +0000) to UTC (offset +0000).)
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==================================================================
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2016-06-14 23:46 = 2016-06-14 23:46
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`)
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}
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func getZone(loc *time.Location) (string, int) {
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return time.Now().In(loc).Zone()
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}
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func checkZones(quiet bool) {
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if quiet {
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return
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}
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toZone, toOff := getZone(toLoc)
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fromZone, fromOff := getZone(fromLoc)
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if toOff == fromOff {
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fmt.Fprintf(os.Stderr, `
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==================================================================
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Note: both input and output timezone offsets are the same --- this
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program may not do what you expect it to.
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(Converting from %s (offset %+05d) to %s (offset %+05d).)
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==================================================================
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`, fromZone, fromOff, toZone, toOff)
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}
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}
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func init() {
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var help, quiet, utc bool
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flag.Usage = func() { usage(os.Stderr) }
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flag.StringVar(&format, "f", format, "time format")
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flag.BoolVar(&help, "h", false, "print usage information")
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flag.StringVar(&outFormat, "o", outFormat, "output time format")
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flag.BoolVar(&quiet, "q", false, "suppress zone check warning")
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flag.BoolVar(&utc, "u", false, "timestamps are in UTC format")
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flag.StringVar(&tz, "z", tz, "time zone to convert from; if blank, the local timezone is used")
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flag.Parse()
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if help {
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if !utc {
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checkZones(quiet)
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}
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usage(os.Stdout)
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os.Exit(0)
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}
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if utc {
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var err error
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toLoc, err = time.LoadLocation(tz)
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if err != nil {
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fmt.Fprintf(os.Stderr, "Malformed timezone %s: %s\n", tz, err)
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os.Exit(1)
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}
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fromLoc = time.UTC
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} else {
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var err error
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fromLoc, err = time.LoadLocation(tz)
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if err != nil {
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fmt.Fprintf(os.Stderr, "Malformed timezone %s: %s\n", tz, err)
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os.Exit(1)
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}
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if fromLoc == time.UTC {
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}
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toLoc = time.UTC
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}
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checkZones(quiet)
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}
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func showTime(t time.Time) {
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fmt.Printf("%s = %s\n", t.Format(outFormat),
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t.In(toLoc).Format(outFormat))
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}
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func dumpTimes(times []string) bool {
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var errored bool
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for _, t := range times {
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u, err := time.ParseInLocation(format, t, fromLoc)
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if err != nil {
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errored = true
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fmt.Fprintf(os.Stderr, "Malformed time %s: %s\n", t, err)
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continue
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}
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showTime(u)
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}
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return errored
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}
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func main() {
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var times []string
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n := flag.NArg()
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switch n {
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case 0:
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showTime(time.Now())
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os.Exit(0)
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case 1:
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if flag.Arg(0) == "-" {
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s := bufio.NewScanner(os.Stdin)
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for s.Scan() {
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times = append(times, s.Text())
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}
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} else if flag.Arg(0) == "help" {
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usageExamples()
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} else {
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times = flag.Args()
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}
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default:
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times = flag.Args()
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}
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if dumpTimes(times) {
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os.Exit(1)
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}
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}
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