File: primes.sh
   1 #!/bin/sh
   2 
   3 # The MIT License (MIT)
   4 #
   5 # Copyright © 2024 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 when not given a count.
  30 #
  31 # The help option is `-h`, `--h`, `-help`, or `--help`.
  32 
  33 
  34 # handle leading options
  35 case "$1" in
  36     -h|--h|-help|--help)
  37         awk '/^# +primes/, /^$/ { gsub(/^# ?/, ""); print }' "$0"
  38         exit 0
  39     ;;
  40 esac
  41 
  42 awk '
  43 BEGIN {
  44     left = 100 * 1000
  45     if (ARGV[1] + 0 != 0) {
  46         left = ARGV[1] + 0
  47         delete ARGV[1]
  48     }
  49 
  50     if (left < 0) {
  51         left = 0
  52     }
  53 
  54     printf "showing first %d prime numbers\n", left > "/dev/stderr"
  55 
  56     if (left > 0) {
  57         print 2
  58         left--
  59     }
  60 
  61     for (n = 3; left > 0; n += 2) {
  62         if (is_prime(n)) {
  63             print n
  64             left--
  65         }
  66     }
  67 
  68     exit
  69 }
  70 
  71 function is_prime(n, max, div) {
  72     if (n < 2) {
  73         return 0
  74     }
  75 
  76     if (n % 2 == 0) {
  77         return n == 2
  78     }
  79 
  80     max = sqrt(n)
  81     for (div = 3; div <= max; div += 2) {
  82         if (n % div == 0) {
  83             return 0
  84         }
  85     }
  86     return 1
  87 }
  88 ' "$@"