File: tcpecho.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 # tcpecho [port] [words...]
  27 #
  28 # Start a TCP server which always replies with a plain-text line made from
  29 # the arguments given after the port number, joined by single spaces.
  30 
  31 
  32 case "$1" in
  33     -h|--h|-help|--help)
  34         awk '/^# +tcpecho /, /^$/ { gsub(/^# ?/, ""); print }' "$0"
  35         exit 0
  36     ;;
  37 esac
  38 
  39 if [ -z "$1" ]; then
  40     awk '/^# +tcpecho /, /^$/ { gsub(/^# ?/, ""); print }' "$0"
  41     exit 0
  42 fi
  43 
  44 port="$1"
  45 [ $# -gt 0 ] && shift
  46 
  47 gawk -v port="${port}" -v msg="$*" '
  48 BEGIN {
  49     if (port < 1 || port > 65535) {
  50         fmt = "\x1b[31m%s is an invalid port number\x1b[0m\n"
  51         printf(fmt, port) > "/dev/stderr"
  52         exit 1
  53     }
  54 
  55     if (msg == "") {
  56         printf "\x1b[31myou forgot the reply message\x1b[0m\n" > "/dev/stderr"
  57         exit 1
  58     }
  59 
  60     gsub(/^ *| *$/, "", msg)
  61 
  62     server = sprintf("/inet/tcp/%d/0/0", port)
  63     PROCINFO[server, "READ_TIMEOUT"] = 200
  64     printf("listening on telnet://localhost:%d\n", port) > "/dev/stderr"
  65 
  66     while (1) {
  67         printf("%s\n", msg) |& server
  68         close(server)
  69     }
  70 
  71     exit
  72 }
  73 '