AUR Byobu updates_available

#!/bin/sh -e
#
#    updates_available: calculate and cache the number of updates available
#    Copyright (C) 2008 Canonical Ltd.
#
#    Authors: Dustin Kirkland <kirkland@canonical.com>
#
#    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, version 3 of the License.
#
#    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 <http://www.gnu.org/licenses/>.

PKG="byobu"
color 2>/dev/null || color() { true; }

if [ "$1" = "--detail" -o "$1" = "--short" ]; then
        if which yaourt >/dev/null; then
                detail=`yaourt -Qu`
                if [ "$1" = "--detail" ]; then
                        printf "$detail"
                else
                        short=`printf "$detail" | wc -l`
                        printf "$short"
                fi
        fi
        exit 0
fi

print_updates() {
        u=$1
        s=$2
        if [ -n "$u" ]; then
                if [ "$u" -gt 0 ]; then
                        printf "$(color b r W)%d$(color -)$(color r W)!" "$u"
                        if [ -n "$s" ]; then
                                if [ "$s" -gt 0 ]; then
                                        printf "!"
                                fi
                        fi
                        printf "$(color -) "
                fi
        fi
}

update_cache() {
        mycache=$1
        # Now we actually have to do hard computational work to calculate updates.
        # Let's try to be "nice" about it:
        renice 10 $$ >/dev/null 2>&1 || true
        ionice -c3 -p $$ >/dev/null 2>&1 || true
        # These are very computationally intensive processes.
        # Background this work, have it write to the cache files,
        # and let the next cache check pick up the results.
        if which yaourt >/dev/null; then
                yaourt -Qu | wc -l > $mycache &
        fi
}

PKG="byobu"

# The following is somewhat Ubuntu and Debian specific (apt).
# I would welcome contributions from other distros to make this
# more distro-agnostic.

[ -d "/var/run/screen/S-$USER" ] && DIR="/var/run/screen/S-$USER" || DIR="$HOME/.byobu"
mycache="$DIR/$PKG.updates-available"

# If mycache is present, use it
[ -r $mycache ] && print_updates `grep "^[0-9]" $mycache | sed "s/ .*$//"`

# Update the cache if necessary
if [ ! -e "$mycache" ] || [ "/var/lib/pacman" -nt "$mycache" ] || [ "/var/lib/pacman/sync" -nt "$mycache" ]; then
        # If apt is newer than mycache, background an update now
        update_cache "$mycache"
fi