$ crontab -l
# -*- conf -*-
PATH=/home/luser/.bin:/bin:/usr/bin:/usr/local/bin

#minute	hour	mday	month	wday	command
*/30	*	*	*	*	slurp git /a/mplayer-build
*/30	*	*	*	*	slurp hg /a/playd.sh

$ cat ~/.bin/slurp
#! /bin/sh

vcs=$1
dir=$2
shift 2

cd "$dir"
case $vcs in
    hg)
	if hg incoming -q --bundle .hgbundle; then
	    hg pull -q .hgbundle
	    rm .hgbundle
	fi
	;;
    git)
	if git fetch 2>&- >&-; then
	    git log --oneline ..origin
	fi
	;;
esac