File: dedup.go
   1 /*
   2 The MIT License (MIT)
   3 
   4 Copyright (c) 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 dedup.go
  30 */
  31 
  32 package main
  33 
  34 import (
  35     "bufio"
  36     "errors"
  37     "io"
  38     "os"
  39 )
  40 
  41 const info = `
  42 dedup [options...] [file...]
  43 
  44 
  45 DEDUPlicate lines prevents the same line from appearing again in the output,
  46 after the first time. Unique lines are remembered across inputs.
  47 
  48 Input is assumed to be UTF-8, and all CRLF byte-pairs are turned into line
  49 feeds by default.
  50 
  51 All (optional) leading options start with either single or double-dash:
  52 
  53     -h, -help    show this help message
  54 `
  55 
  56 type stringSet map[string]struct{}
  57 
  58 func main() {
  59     buffered := false
  60     args := os.Args[1:]
  61 
  62     if len(args) > 0 {
  63         switch args[0] {
  64         case `-b`, `--b`, `-buffered`, `--buffered`:
  65             buffered = true
  66             args = args[1:]
  67 
  68         case `-h`, `--h`, `-help`, `--help`:
  69             os.Stdout.WriteString(info[1:])
  70             return
  71         }
  72     }
  73 
  74     if len(args) > 0 && args[0] == `--` {
  75         args = args[1:]
  76     }
  77 
  78     liveLines := !buffered
  79     if !buffered {
  80         if _, err := os.Stdout.Seek(0, io.SeekCurrent); err == nil {
  81             liveLines = false
  82         }
  83     }
  84 
  85     err := run(os.Stdout, args, liveLines)
  86     if err != nil && err != io.EOF {
  87         os.Stderr.WriteString(err.Error())
  88         os.Stderr.WriteString("\n")
  89         os.Exit(1)
  90         return
  91     }
  92 }
  93 
  94 func run(w io.Writer, args []string, live bool) error {
  95     files := make(stringSet)
  96     lines := make(stringSet)
  97     bw := bufio.NewWriter(w)
  98     defer bw.Flush()
  99 
 100     for _, name := range args {
 101         if _, ok := files[name]; ok {
 102             continue
 103         }
 104         files[name] = struct{}{}
 105 
 106         if err := handleFile(bw, name, lines, live); err != nil {
 107             return err
 108         }
 109     }
 110 
 111     if len(args) == 0 {
 112         return dedup(bw, os.Stdin, lines, live)
 113     }
 114     return nil
 115 }
 116 
 117 func handleFile(w *bufio.Writer, name string, got stringSet, live bool) error {
 118     if name == `` || name == `-` {
 119         return dedup(w, os.Stdin, got, live)
 120     }
 121 
 122     f, err := os.Open(name)
 123     if err != nil {
 124         return errors.New(`can't read from file named "` + name + `"`)
 125     }
 126     defer f.Close()
 127 
 128     return dedup(w, f, got, live)
 129 }
 130 
 131 func dedup(w *bufio.Writer, r io.Reader, got stringSet, live bool) error {
 132     const gb = 1024 * 1024 * 1024
 133     sc := bufio.NewScanner(r)
 134     sc.Buffer(nil, 8*gb)
 135 
 136     for sc.Scan() {
 137         line := sc.Text()
 138         if _, ok := got[line]; ok {
 139             continue
 140         }
 141         got[line] = struct{}{}
 142 
 143         w.Write(sc.Bytes())
 144         if w.WriteByte('\n') != nil {
 145             return io.EOF
 146         }
 147 
 148         if !live {
 149             continue
 150         }
 151 
 152         if err := w.Flush(); err != nil {
 153             return io.EOF
 154         }
 155     }
 156 
 157     return sc.Err()
 158 }