File: first.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 # first [options...] [max lines...] [files...]
  27 #
  28 # Limit output to only the first n given lines, using the leading number given,
  29 # or the first line by default. This is just more intuitive than using the
  30 # basic command `head -n`.
  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 lines=1
  39 got_lines=0
  40 
  41 while [ $# -gt 0 ]; do
  42     case "$1" in
  43         -b|--b|-buffered|--buffered) buffered=1; shift; continue ;;
  44 
  45         -h|--h|-help|--help)
  46             awk '/^# +first /, /^$/ { gsub(/^# ?/, ""); print }' "$0"
  47             exit 0
  48         ;;
  49 
  50         -n)
  51             if [ $# -lt 2 ]; then
  52                 printf "%s: missing number for option -n\n" "$0" >&2
  53                 exit 1
  54             fi
  55             if echo "$2" | grep -q -E '^\+?[0-9]+$'; then
  56                 lines="$2"
  57                 shift 2
  58                 got_lines=1
  59             else
  60                 printf "%s: %s isn't a valid number\n" "$0" "$2" >&2
  61                 exit 1
  62             fi
  63             continue
  64         ;;
  65 
  66         -) break ;;
  67 
  68         --) shift; break ;;
  69 
  70         -*)
  71             printf "%s: unsupported option %s\n" "$0" "$1" >&2
  72             exit 1
  73         ;;
  74     esac
  75 
  76     break
  77 done
  78 
  79 if [ "${got_lines}" -eq 0 ]; then
  80     if echo "$1" | grep -q -E '^\+?[0-9]+$'; then
  81         lines="$1"
  82         shift
  83     fi
  84 fi
  85 
  86 # head -n "${lines}" "$@"
  87 
  88 # show all non-existing files given
  89 failed=0
  90 for arg in "$@"; do
  91     [ "${arg}" = '-' ] && continue
  92     [ -e "${arg}" ] && continue
  93     printf "%s: no file named \"%s\"\n" "$0" "${arg}" >&2
  94     failed=1
  95 done
  96 
  97 [ "${failed}" -gt 0 ] && exit 2
  98 
  99 flush=0
 100 if [ "${buffered}" -eq 0 ] && { [ -p /dev/stdout ] || [ -t 1 ]; }; then
 101     flush=1
 102 fi
 103 
 104 awk -v flush="${flush}" -v n="${lines}" '
 105     NR > n { exit }
 106     { print; if (flush) fflush() }
 107     NR >= n { exit }
 108 ' "$@"