#!/bin/sh
# join-v-1 - Filter out a set of items from another set of items.

# Copyright (C) 2021 Free Software Foundation, Inc.
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <https://www.gnu.org/licenses/>.

# Usage: join-v-1 FILE1 FILE2
# Produces on stdout a list of items that are contained in FILE1 but not
# contained in FILE2.  The items are strings without whitespace.
# FILE1 and FILE2 contain such items, one per line, sorted according to
# the current locale.
# FILE1 or FILE2 can be specified as '-', which denotes standard input.

# The 'join' program does not exist on all platforms.  Where it exists,
# we can use it.
if (type join) >/dev/null 2>&1; then
  join -v 1 "$1" "$2"
else
  # Two solutions based on awk, by Bernhard Voelker <mail@bernhard-voelker.de>.
  if true; then
    awk -v keyfile="$2" '
      BEGIN { while ((getline < keyfile) > 0) k[$1]=1 }
      !k[$1]
      ' "$1"
  else
    awk '
      keys { k[$1]=1; next }
      !k[$1]
      ' keys=1 "$2" keys=0 "$1"
  fi
fi