File: dedup.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 dedup.
  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 dedup.go
  32 */
  33 
  34 package main
  35 
  36 import (
  37     "bufio"
  38     "errors"
  39     "io"
  40     "os"
  41 )
  42 
  43 // Note: the code is avoiding using the fmt package to save hundreds of
  44 // kilobytes on the resulting executable, which is a noticeable difference.
  45 
  46 const info = `
  47 dedup [options...] [file...]
  48 
  49 
  50 DEDUPlicate lines prevents the same line from appearing again, after the
  51 first time. Unique lines are remembered across inputs.
  52 
  53 Input is assumed to be UTF-8, and all CRLF byte-pairs are turned into line
  54 feeds.
  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     seen := make(map[string]struct{})
  87     bw := bufio.NewWriter(w)
  88     defer bw.Flush()
  89 
  90     if len(args) == 0 {
  91         return dedup(bw, os.Stdin, seen)
  92     }
  93 
  94     for _, name := range args {
  95         if err := handleFile(bw, name, seen); err != nil {
  96             return err
  97         }
  98     }
  99     return nil
 100 }
 101 
 102 func handleFile(w *bufio.Writer, name string, seen map[string]struct{}) error {
 103     if name == `` || name == `-` {
 104         return dedup(w, os.Stdin, seen)
 105     }
 106 
 107     f, err := os.Open(name)
 108     if err != nil {
 109         return errors.New(`can't read from file named "` + name + `"`)
 110     }
 111     defer f.Close()
 112 
 113     return dedup(w, f, seen)
 114 }
 115 
 116 // isActualError is to figure out whether not to ignore an error, and thus
 117 // show it as an error message
 118 func isActualError(err error) bool {
 119     return err != nil && err != io.EOF && err != errNoMoreOutput
 120 }
 121 
 122 func dedup(w *bufio.Writer, r io.Reader, seen map[string]struct{}) error {
 123     const gb = 1024 * 1024 * 1024
 124     sc := bufio.NewScanner(r)
 125     sc.Buffer(nil, 8*gb)
 126 
 127     for sc.Scan() {
 128         line := sc.Text()
 129         if _, ok := seen[line]; ok {
 130             continue
 131         }
 132 
 133         w.Write(sc.Bytes())
 134         if err := w.WriteByte('\n'); err != nil {
 135             // a write error may be the consequence of stdout being closed,
 136             // perhaps by another app along a pipe
 137             return errNoMoreOutput
 138         }
 139         w.Flush()
 140 
 141         seen[line] = struct{}{}
 142     }
 143 
 144     return sc.Err()
 145 }