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