Add utc for time -> UTC conversions.

README.md

@@ -29,6 +29,7 @@ Contents:
         stealchain/ Dump the verified chain from a TLS
                     connection.
         tlskeypair/ Check whether a TLS certificate and key file match.
+		utc/        Convert times to UTC.
     die/            Death of a program.
 	fileutil/       Common file functions.
     lib/            Commonly-useful functions for writing Go programs.

cmd/utc/README

@@ -0,0 +1,48 @@
+utc: convert times to UTC
+
+utc converts times to UTC. If no arguments are provided, prints the
+current time in UTC. If the only time provided is "-", reads
+newline-separated timestamps from standard input.
+
+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.
+	-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.
+
+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
+
+
+
+	  
+	

cmd/utc/main.go

@@ -0,0 +1,162 @@
+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)
+	}
+}