File: decap.sh
   1 #!/bin/sh
   2 
   3 # The MIT License (MIT)
   4 #
   5 # Copyright (c) 2026 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 # decap [options...] [max lines...] [command...] [command args...]
  27 #
  28 # DECAPitate emits the first n lines from the standard input, handing the rest
  29 # (if any) to the command given. If a leading number isn't given, the default
  30 # is to `decapitate` just the first line.
  31 #
  32 # The options are, available both in single and double-dash versions
  33 #
  34 #   -h, -help    show this help message
  35 
  36 
  37 buffered=0
  38 
  39 case "$1" in
  40     -b|--b|-buffered|--buffered)
  41         buffered=1
  42         shift
  43     ;;
  44 
  45     -h|--h|-help|--help)
  46         awk '/^# +decap /, /^$/ { gsub(/^# ?/, ""); print }' "$0"
  47         exit 0
  48     ;;
  49 
  50     --) ;;
  51 
  52     -*)
  53         printf "unsupported option '%s'\n" "$1" >&2
  54         exit 1
  55     ;;
  56 esac
  57 
  58 lines=1
  59 if echo "$1" | grep -q -E '^\+?[0-9]+$'; then
  60     lines="$1"
  61     shift
  62 fi
  63 
  64 [ "$1" = '--' ] && shift
  65 
  66 flush=0
  67 if [ "${buffered}" -eq 0 ] && { [ -p /dev/stdout ] || [ -t 1 ]; }; then
  68     flush=1
  69 fi
  70 
  71 if [ $# -eq 0 ]; then
  72     awk -v flush="${flush}" -v n="${lines}" '
  73         NR > n { exit }
  74         { print; if (flush) fflush() }
  75         NR >= n { exit }
  76     '
  77 else
  78     awk -v flush="${flush}" -v n="${lines}" -v command="$*" '
  79         NR > n { print | command; next }
  80         { print; if (flush) fflush() }
  81     '
  82 fi