--- tl-dbus-launch.sh.orig	2014-10-29 09:47:52.000000000 -0400
+++ tl-dbus-launch.sh	2015-01-28 23:21:20.000000000 -0500
@@ -8,6 +8,6 @@
 #
 
 # Start DBUS, if not already started
-if type dbus-launch && test -z "${DBUS_SESSION_BUS_ADDRESS}" ; then
+if type dbus-launch && test -z ${DBUS_SESSION_BUS_ADDRESS+x} ; then
     eval `dbus-launch --sh-syntax --exit-with-session`
 fi
--- tl-homecreatefilter.sh.orig	2014-10-29 09:48:07.000000000 -0400
+++ tl-homecreatefilter.sh	2015-01-28 23:23:38.000000000 -0500
@@ -6,7 +6,7 @@
 
 ID=`id -u`
 
-if [ -z "${TLPREFIX}" ]; then
+if [ -z ${TLPREFIX+x} ]; then
     echo "Cannot work without TLPREFIX. Exiting."
 elif [ "${ID}" -eq 0 ] ; then
     echo "Root user detected - skipping homecreatefilter"
--- tl-kinit.sh.orig	2014-10-29 09:47:52.000000000 -0400
+++ tl-kinit.sh	2015-01-28 23:16:10.000000000 -0500
@@ -8,7 +8,7 @@
 #
 
 if type kinit; then
-    if [ -z "${KRB5CCNAME}" ]; then
+    if [ -z ${KRB5CCNAME+x} ]; then
         export KRB5CCNAME="${TLSESSIONDATA}/krb5cc"
     fi
     # -l without argument gives usage with both MIT and Heimdal
--- tl-lp-redir-launch.orig	2014-10-29 10:02:57.000000000 -0400
+++ tl-lp-redir-launch	2015-01-28 23:24:04.000000000 -0500
@@ -7,7 +7,7 @@
 # action: Setting up printer port redirection
 #
 
-if [ -z "${TLPREFIX}" ]; then
+if [ -z ${TLPREFIX+x} ]; then
     echo "Cannot work without TLPREFIX. Exiting."
 else
     "${TLPREFIX}/bin/tl-while-x11" "${TLPREFIX}/libexec/tl-lp-redir" "${TLSESSIONDATA}/dev/lp0" thinlocal &
--- tl-run-xlogout.d.orig	2014-10-29 09:48:01.000000000 -0400
+++ tl-run-xlogout.d	2015-01-28 23:24:30.000000000 -0500
@@ -4,7 +4,7 @@
 # Copyright 2002-2014 Cendio AB.
 # For more information, see http://www.cendio.com
 
-if [ -z "${TLPREFIX}" ]; then
+if [ -z ${TLPREFIX+x} ]; then
     echo "Cannot work without TLPREFIX. Exiting."
     exit 1
 fi
--- tl-run-xstartup.d.orig	2014-10-29 09:48:01.000000000 -0400
+++ tl-run-xstartup.d	2015-01-28 23:25:19.000000000 -0500
@@ -9,14 +9,14 @@
 # executed for testing.
 #
 
-if [ -z "${TLPREFIX}" ]; then
+if [ -z ${TLPREFIX+x} ]; then
     echo "Cannot work without TLPREFIX. Exiting."
     exit 1
 fi
 
 source ${TLPREFIX}/libexec/functions
 
-if [ -z "${TLSESSIONDATA}" ]; then
+if [ -z ${TLSESSIONDATA+x} ]; then
     echo "TLSESSIONDATA is not set. Are you in a proper ThinLinc session?"
     exit 1
 fi
--- tl-serial-redir.sh.orig	2014-10-29 09:47:52.000000000 -0400
+++ tl-serial-redir.sh	2015-01-28 23:25:41.000000000 -0500
@@ -7,7 +7,7 @@
 # action: Setting up serial port redirection
 #
 
-if [ -z "${TLPREFIX}" ]; then
+if [ -z ${TLPREFIX+x} ]; then
     echo "Cannot work without TLPREFIX. Exiting."
 else
     if [ "${LD_PRELOAD}" ]; then
--- tl-ssh-askpass.orig	2015-01-28 23:22:47.000000000 -0500
+++ tl-ssh-askpass	2015-01-28 23:26:03.000000000 -0500
@@ -8,7 +8,7 @@
 ORIGIN=`(cd "\`dirname \"$ORIGIN\"\`"; pwd -P 2>/dev/null || pwd)`
 
 # Allow user to select which Python to use
-if [ -z "${PYTHON}" ]; then
+if [ -z ${PYTHON+x} ]; then
     PYTHON="python"
 fi