File: primes.sh
   1 #!/bin/sh
   2 
   3 # The MIT License (MIT)
   4 #
   5 # Copyright © 2020-2025 pacman64
   6 #
   7 # Permission is hereby granted, free of charge, to any person obtaining a copy
   8 # of this software and associated documentation files (the “Software”), to deal
   9 # in the Software without restriction, including without limitation the rights
  10 # to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  11 # copies of the Software, and to permit persons to whom the Software is
  12 # furnished to do so, subject to the following conditions:
  13 #
  14 # The above copyright notice and this permission notice shall be included in
  15 # all copies or substantial portions of the Software.
  16 #
  17 # THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  18 # IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  19 # FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  20 # AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  21 # LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  22 # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  23 # SOFTWARE.
  24 
  25 
  26 # primes [options...] [count...]
  27 #
  28 # Find the first n prime numbers, emitting each one on its own line, with a
  29 # default of 100 thousand primes when not given a count.
  30 #
  31 # The help option is `-h`, `--h`, `-help`, or `--help`.
  32 
  33 
  34 case "$1" in
  35     -h|--h|-help|--help)
  36         awk '/^# +primes /, /^$/ { gsub(/^# ?/, ""); print }' "$0"
  37         exit 0
  38     ;;
  39 esac
  40 
  41 awk '
  42     BEGIN {
  43         left = 100 * 1000
  44         if (ARGV[1] ~ /^0+/ || ARGV[1] + 0 != 0) {
  45             left = ARGV[1] + 0
  46             delete ARGV[1]
  47         }
  48 
  49         if (left < 0) left = 0
  50 
  51         printf "showing first %d prime numbers\n", left > "/dev/stderr"
  52 
  53         if (left > 0) {
  54             print 2
  55             left--
  56         }
  57 
  58         for (n = 3; left > 0; n += 2) {
  59             if (positive_odd_is_prime(n)) {
  60                 print n
  61                 left--
  62             }
  63         }
  64 
  65         exit
  66     }
  67 
  68     function positive_odd_is_prime(n, max, div) {
  69         max = sqrt(n)
  70         for (div = 3; div <= max; div += 2) {
  71             if (n % div == 0) {
  72                 return 0
  73             }
  74         }
  75         return 1
  76     }
  77 ' "$@"