/opt/kde3/share/config/kdm/xsession

#! /bin/sh
# Xsession - run as user

# redirect errors to a file in user's home directory if we can
for errfile in "$HOME/.xsession-errors" "${TMPDIR-/tmp}/xses-$USER" "/tmp/xses-$USER"
do
 * * * *if ( cp /dev/null "$errfile" 2> /dev/null )
 * * * *then
 * * * * * * * *chmod 600 "$errfile"
 * * * * * * * *exec > "$errfile" 2>&1
 * * * * * * * *break
 * * * *fi
done

DM_PATH=$PATH
PATH=
test -f /etc/profile && . /etc/profile
test -f $HOME/.profile && . $HOME/.profile
IFS_SAVE=$IFS
IFS=:
for i in $DM_PATH; do
 * *case :$PATH: in
 * * **:$i:*);;
 * * *::) PATH=$i;;
 * * **) PATH=$PATH:$i;;
 * *esac
done
IFS=$IFS_SAVE
export PATH

test -f /etc/xprofile && . /etc/xprofile
test -f $HOME/.xprofile && . $HOME/.xprofile

case $1 in
 * *"")
 * * * *exec xmessage -center -buttons OK:0 -default OK "Sorry, $DESKTOP_SESSION is no valid session."
 * * * ;;
 * *failsafe)
 * * * *exec xterm -geometry 80x24-0-0
 * * * ;;
 * *custom)
 * * * *exec $HOME/.xsession
 * * * ;;
 * *default)
 * * * *exec startkde
 * * * ;;
 * **)
 * * * *eval exec "$1"
 * * * ;;
esac
exec xmessage -center -buttons OK:0 -default OK "Sorry, cannot execute $1. Check $DESKTOP_SESSION.desktop."

Great sample, thanks for this.