update-alternatives: Script copied from opkg

The update-alternatives script is being moved from opkg to opkg-utils to break
possible circular dependencies in openembedded. As opkg will depend on
libarchive soon, and may depend on other packages if certain options are
enabled, opkg cannot itself provide update-alternatives if its dependencies
require update-alternatives.

opkg-utils has minimal build-time dependencies and so is a good place to put the
update-alternatives script.

Signed-off-by: Paul Barker <paul@paulbarker.me.uk>

Makefile

@@ -1,6 +1,6 @@
 UTILS = opkg-build opkg-unbuild opkg-compare-versions opkg-make-index opkg.py \
         opkg-list-fields arfile.py opkg-buildpackage opkg-diff opkg-extract-file opkg-show-deps \
-        opkg-compare-indexes opkg-compare-versions.sh
+        opkg-compare-indexes opkg-compare-versions.sh update-alternatives
 
 DESTDIR=
 PREFIX=/usr/local

update-alternatives

@@ -0,0 +1,190 @@
+#!/bin/sh
+# update-alternatives
+#
+# Copyright (C) 2001 Carl D. Worth
+#
+# This program was inspired by the Debian update-alternatives program
+# which is Copyright (C) 1995 Ian Jackson. This version of
+# update-alternatives is command-line compatible with Debian's for a
+# subset of the options, (only --install, --remove, and --help)
+#
+# 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 2, 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.
+
+set -e
+
+# admin dir
+ad="$OPKG_OFFLINE_ROOT/usr/lib/opkg/alternatives"
+
+usage() {
+	echo "update-alternatives: $*
+
+Usage: update-alternatives --install <link> <name> <path> <priority>
+       update-alternatives --remove <name> <path>
+       update-alternatives --help
+<link> is the link pointing to the provided path (ie. /usr/bin/foo).
+<name> is the name in $ad/alternatives (ie. foo)
+<path> is the name referred to (ie. /usr/bin/foo-extra-spiffy)
+<priority> is an integer; options with higher numbers are chosen.
+" >&2
+	exit 2
+}
+
+quit() {
+	echo "update-alternatives: $*" >&2
+	exit 2
+}
+
+register_alt() {
+	[ $# -lt 2 ] && return 1
+	local name="$1"
+	local link="$2"
+
+	if [ ! -d $ad ]; then
+		mkdir -p $ad
+	fi
+
+	if [ -e "$ad/$name" ]; then
+		local olink=`head -n 1 $ad/$name`
+		if [ "$link" != "$olink" ]; then
+			echo "update-alternatives: Error: cannot register alternative $name to $link since it is already registered to $olink" >&2
+			return 1
+		fi
+	else
+		echo "$link" > "$ad/$name"
+	fi
+
+	return 0
+}
+
+protect_slashes() {
+	sed -e 's/\//\\\//g'
+}
+
+remove_alt() {
+	[ $# -lt 2 ] && return 1
+	local name="$1"
+	local path="$2"
+
+	[ ! -f $ad/$name ] && return 0
+
+	path=`echo $path | protect_slashes`
+	sed -ne "/^$path\>.*/!p" $ad/$name > $ad/$name.new
+	mv $ad/$name.new $ad/$name
+}
+
+add_alt() {
+	[ $# -lt 3 ] && return 1
+	local name="$1"
+	local path="$2"
+	local priority="$3"
+	remove_alt $name $path
+	echo "$path $priority" >> $ad/$name
+}
+
+find_best_alt() {
+	[ $# -lt 1 ] && return 1
+	[ ! -f $ad/$name ] && return 0
+
+	link=$OPKG_OFFLINE_ROOT/`head -n 1 $ad/$name`
+
+	prio=`sed -ne "1!p" $ad/$name | sed -e "s/\(.*\) \(.*\)/\2 \1/g" | sort -nr | head -n 1 | sed 's/ [^ ]*$//'`
+	if [ -z "$prio" ]; then
+		echo "update-alternatives: removing $link as no more alternatives exist for it"
+		rm $ad/$name
+		if [ -L $link ]; then
+			rm $link
+		fi
+		return 0
+	fi
+
+	## Find last line with highest priority.
+	path=`grep "${prio}$" $ad/$name | tail -n 1 | sed 's/ [^ ]*$//'`
+
+	if [ ! -e $link -o -L $link ]; then
+		local link_dir=`dirname $link`
+		if [ ! -d $link_dir ]; then
+			mkdir -p $link_dir
+		fi
+		ln -snf $path $link
+		echo "update-alternatives: Linking $link to $path"
+	else
+		echo "update-alternatives: Error: not linking $link to $path since $link exists and is not a link"
+		return 1
+	fi
+
+	return 0
+}
+
+do_install() {
+	if [ $# -lt 4 ]; then
+		usage "--install needs <link> <name> <path> <priority>"
+	fi
+	local link="$1"
+	local name="$2"
+	local path="$3"
+	local priority="$4"
+
+	path=`echo $path | sed 's|/\+|/|g'`
+
+	# This is a bad hack, but I haven't thought of a cleaner solution yet...
+	[ -n "$OPKG_OFFLINE_ROOT" ] && path=`echo $path | sed "s|^$OPKG_OFFLINE_ROOT/*|/|"`
+
+	register_alt $name $link
+	add_alt $name $path $priority
+	find_best_alt $name
+}
+
+do_remove() {
+	if [ $# -lt 2 ]; then
+		usage "--remove needs <name> <path>"
+	fi
+	local name="$1"
+	local path="$2"
+
+	path=`echo $path | sed 's|/\+|/|g'`
+
+	# This is a bad hack, but I haven't thought of a cleaner solution yet...
+	[ -n "$OPKG_OFFLINE_ROOT" ] && path=`echo $path | sed "s|^$OPKG_OFFLINE_ROOT/*|/|"`
+
+	remove_alt $name $path
+	find_best_alt $name
+}
+
+###
+# update-alternatives "main"
+###
+
+while [ $# -gt 0 ]; do
+	arg="$1"
+	shift
+
+	case $arg in
+	--help)
+		usage "help:"
+		exit 0
+		;;
+	--install)
+		do_install $*
+		exit $?
+		;;
+	--remove)
+		do_remove $*
+		exit $?
+		;;
+	*)
+		usage "unknown argument \`$arg'"
+		;;
+	esac
+done
+
+usage "at least one of --install or --remove must appear"
+
+exit 0