File: timestamp.go
   1 /*
   2 The MIT License (MIT)
   3 
   4 Copyright © 2020-2025 pacman64
   5 
   6 Permission is hereby granted, free of charge, to any person obtaining a copy of
   7 this software and associated documentation files (the “Software”), to deal
   8 in the Software without restriction, including without limitation the rights to
   9 use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
  10 of the Software, and to permit persons to whom the Software is furnished to do
  11 so, subject to the following conditions:
  12 
  13 The above copyright notice and this permission notice shall be included in all
  14 copies or substantial portions of the Software.
  15 
  16 THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  17 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18 FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  19 AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  20 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  21 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  22 SOFTWARE.
  23 */
  24 
  25 /*
  26 Single-file source-code for timestamp.
  27 
  28 To compile a smaller-sized command-line app, you can use the `go` command as
  29 follows:
  30 
  31 go build -ldflags "-s -w" -trimpath timestamp.go
  32 */
  33 
  34 package main
  35 
  36 import (
  37     "bufio"
  38     "errors"
  39     "io"
  40     "os"
  41     "time"
  42 )
  43 
  44 // Note: the code is avoiding using the fmt package to save hundreds of
  45 // kilobytes on the resulting executable, which is a noticeable difference.
  46 
  47 const info = `
  48 timestamp [options...] [file...]
  49 
  50 
  51 Start each line with a timestamp, followed by a tab, and then the line.
  52 
  53 Input is assumed to be UTF-8, and all CRLF byte-pairs are turned into line
  54 feeds. Leading BOM (byte-order marks) on first lines are also ignored.
  55 
  56 All (optional) leading options start with either single or double-dash:
  57 
  58     -h          show this help message
  59     -help       show this help message
  60 `
  61 
  62 const errorStyle = "\x1b[31m"
  63 
  64 // errNoMoreOutput is a dummy error, whose message is ignored, and which
  65 // causes the app to quit immediately and successfully
  66 var errNoMoreOutput = errors.New(`no more output`)
  67 
  68 func main() {
  69     if len(os.Args) > 1 {
  70         switch os.Args[1] {
  71         case `-h`, `--h`, `-help`, `--help`:
  72             os.Stderr.WriteString(info[1:])
  73             return
  74         }
  75     }
  76 
  77     if err := run(os.Stdout, os.Args[1:]); isActualError(err) {
  78         os.Stderr.WriteString(errorStyle)
  79         os.Stderr.WriteString(err.Error())
  80         os.Stderr.WriteString("\x1b[0m\n")
  81         os.Exit(1)
  82     }
  83 }
  84 
  85 func run(w io.Writer, args []string) error {
  86     bw := bufio.NewWriter(w)
  87     defer bw.Flush()
  88 
  89     if len(args) == 0 {
  90         return timestamp(bw, os.Stdin)
  91     }
  92 
  93     for _, name := range args {
  94         if err := handleFile(bw, name); err != nil {
  95             return err
  96         }
  97     }
  98     return nil
  99 }
 100 
 101 func handleFile(w *bufio.Writer, name string) error {
 102     if name == `` || name == `-` {
 103         return timestamp(w, os.Stdin)
 104     }
 105 
 106     f, err := os.Open(name)
 107     if err != nil {
 108         return errors.New(`can't read from file named "` + name + `"`)
 109     }
 110     defer f.Close()
 111 
 112     return timestamp(w, f)
 113 }
 114 
 115 // isActualError is to figure out whether not to ignore an error, and thus
 116 // show it as an error message
 117 func isActualError(err error) bool {
 118     return err != nil && err != io.EOF && err != errNoMoreOutput
 119 }
 120 
 121 func timestamp(w *bufio.Writer, r io.Reader) error {
 122     const gb = 1024 * 1024 * 1024
 123     sc := bufio.NewScanner(r)
 124     sc.Buffer(nil, 8*gb)
 125 
 126     var buf [64]byte
 127 
 128     for sc.Scan() {
 129         now := time.Now()
 130         w.WriteString("\x1b[48;2;218;218;218m\x1b[38;2;0;95;153m")
 131         w.Write(now.AppendFormat(buf[:0], `2006-01-02 15:04:05`))
 132         w.WriteString("\x1b[0m\t")
 133         // w.Write(now.AppendFormat(buf[:0], `2006-01-02 15:04:05`))
 134         // w.Write([]byte{'\t'})
 135 
 136         w.Write(sc.Bytes())
 137         if err := w.WriteByte('\n'); err != nil {
 138             // a write error may be the consequence of stdout being closed,
 139             // perhaps by another app along a pipe
 140             return errNoMoreOutput
 141         }
 142         w.Flush()
 143     }
 144 
 145     return sc.Err()
 146 }