File: timestamp.go
   1 /*
   2 The MIT License (MIT)
   3 
   4 Copyright © 2026 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 To compile a smaller-sized command-line app, you can use the `go` command as
  27 follows:
  28 
  29 go build -ldflags "-s -w" -trimpath timestamp.go
  30 */
  31 
  32 package main
  33 
  34 import (
  35     "bufio"
  36     "errors"
  37     "io"
  38     "os"
  39     "time"
  40 )
  41 
  42 // Note: the code is avoiding using the fmt package to save hundreds of
  43 // kilobytes on the resulting executable, which is a noticeable difference.
  44 
  45 const info = `
  46 timestamp [options...] [file...]
  47 
  48 
  49 Start each line with a timestamp, followed by a tab, and then the line.
  50 
  51 Input is assumed to be UTF-8, and all CRLF byte-pairs are turned into line
  52 feeds. Leading BOM (byte-order marks) on first lines are also ignored.
  53 
  54 All (optional) leading options start with either single or double-dash:
  55 
  56     -h          show this help message
  57     -help       show this help message
  58 `
  59 
  60 // errNoMoreOutput is a dummy error whose message is ignored, and which
  61 // causes the app to quit immediately and successfully
  62 var errNoMoreOutput = errors.New(`no more output`)
  63 
  64 func main() {
  65     if len(os.Args) > 1 {
  66         switch os.Args[1] {
  67         case `-h`, `--h`, `-help`, `--help`:
  68             os.Stdout.WriteString(info[1:])
  69             return
  70         }
  71     }
  72 
  73     if err := run(os.Stdout, os.Args[1:]); isActualError(err) {
  74         os.Stderr.WriteString(err.Error())
  75         os.Stderr.WriteString("\n")
  76         os.Exit(1)
  77     }
  78 }
  79 
  80 func run(w io.Writer, args []string) error {
  81     bw := bufio.NewWriter(w)
  82     defer bw.Flush()
  83 
  84     if len(args) == 0 {
  85         return timestamp(bw, os.Stdin)
  86     }
  87 
  88     for _, name := range args {
  89         if err := handleFile(bw, name); err != nil {
  90             return err
  91         }
  92     }
  93     return nil
  94 }
  95 
  96 func handleFile(w *bufio.Writer, name string) error {
  97     if name == `` || name == `-` {
  98         return timestamp(w, os.Stdin)
  99     }
 100 
 101     f, err := os.Open(name)
 102     if err != nil {
 103         return errors.New(`can't read from file named "` + name + `"`)
 104     }
 105     defer f.Close()
 106 
 107     return timestamp(w, f)
 108 }
 109 
 110 // isActualError is to figure out whether not to ignore an error, and thus
 111 // show it as an error message
 112 func isActualError(err error) bool {
 113     return err != nil && err != io.EOF && err != errNoMoreOutput
 114 }
 115 
 116 func timestamp(w *bufio.Writer, r io.Reader) error {
 117     const gb = 1024 * 1024 * 1024
 118     sc := bufio.NewScanner(r)
 119     sc.Buffer(nil, 8*gb)
 120 
 121     var buf [64]byte
 122 
 123     for sc.Scan() {
 124         now := time.Now()
 125         w.WriteString("\x1b[48;2;218;218;218m\x1b[38;2;0;95;153m")
 126         w.Write(now.AppendFormat(buf[:0], `2006-01-02 15:04:05`))
 127         w.WriteString("\x1b[0m\t")
 128         // w.Write(now.AppendFormat(buf[:0], `2006-01-02 15:04:05`))
 129         // w.Write([]byte{'\t'})
 130 
 131         w.Write(sc.Bytes())
 132         w.WriteByte('\n')
 133         if err := w.Flush(); err != nil {
 134             // a write error may be the consequence of stdout being closed,
 135             // perhaps by another app along a pipe
 136             return errNoMoreOutput
 137         }
 138     }
 139 
 140     return sc.Err()
 141 }