diff --git a/debian/changelog b/debian/changelog
index b4f3c28..3baa874 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -14,6 +14,8 @@ xen-tools (4.4~dev-1) UNRELEASED; urgency=low
   * xen-list-images now displays a unit after the memory size
   * Drop support for memory size in kilobytes in
     xen-create-image, neither xt-create-xen-config nor xm support it.
+  * Refactoring: Replace all occurrences of "! -z" by "-n" in hooks and
+    bash completion.
 
  -- Axel Beckert <abe@debian.org>  Fri, 23 Aug 2013 21:13:07 +0200
 
diff --git a/hooks/centos-5/25-setup-kernel b/hooks/centos-5/25-setup-kernel
index c65979e..268ef9f 100755
--- a/hooks/centos-5/25-setup-kernel
+++ b/hooks/centos-5/25-setup-kernel
@@ -41,7 +41,7 @@ EOF
 for i in `seq 1 $NUMPARTITIONS`; do
   echo -n "/dev/xvde$i " >> ${prefix}/etc/fstab
   eval part=\$PARTITION$i
-  if [ ! -z "`echo $part | grep swap`" ]; then
+  if [ -n "`echo $part | grep swap`" ]; then
      echo "none swap ws 0 0" >> ${prefix}/etc/fstab
   else
      echo $part | awk -F: '{print $4,$3,$5,0,1}' >> ${prefix}/etc/fstab
diff --git a/hooks/centos-6/25-setup-kernel b/hooks/centos-6/25-setup-kernel
index 2c99703..972ae21 100755
--- a/hooks/centos-6/25-setup-kernel
+++ b/hooks/centos-6/25-setup-kernel
@@ -41,7 +41,7 @@ EOF
 for i in `seq 1 $NUMPARTITIONS`; do
   echo -n "/dev/sda$i " >> ${prefix}/etc/fstab
   eval part=\$PARTITION$i
-  if [ ! -z "`echo $part | grep swap`" ]; then
+  if [ -n "`echo $part | grep swap`" ]; then
      echo "none swap ws 0 0" >> ${prefix}/etc/fstab
   else
      echo $part | awk -F: '{print $4,$3,$5,0,1}' >> ${prefix}/etc/fstab
diff --git a/hooks/common.sh b/hooks/common.sh
index d6893cb..7b571a7 100755
--- a/hooks/common.sh
+++ b/hooks/common.sh
@@ -24,7 +24,7 @@ logMessage ()
 {
     message="$*"
 
-    if [ ! -z "${verbose}" ]; then
+    if [ -n "${verbose}" ]; then
         echo $message
     fi
 }
diff --git a/hooks/common/30-disable-gettys b/hooks/common/30-disable-gettys
index 6edc80b..db4707a 100755
--- a/hooks/common/30-disable-gettys
+++ b/hooks/common/30-disable-gettys
@@ -49,7 +49,7 @@ rm -f ${prefix}/etc/event.d/tty[!1]
 #
 #  Are we using an alternative serial device?
 #
-if [ ! -z "${serial_device}" ]; then
+if [ -n "${serial_device}" ]; then
 
     serial_device=`basename ${serial_device}`
 
diff --git a/hooks/common/40-setup-networking-deb b/hooks/common/40-setup-networking-deb
index d8785ae..4cbc83c 100755
--- a/hooks/common/40-setup-networking-deb
+++ b/hooks/common/40-setup-networking-deb
@@ -71,7 +71,7 @@ setupStaticNetworking ()
     #  if $p2p is set then add a "pointopoint" setting.
     #
     point='';
-    if [ ! -z "${p2p}" ]; then
+    if [ -n "${p2p}" ]; then
         point="pointopoint ${p2p}"
     else
         point=''
@@ -81,7 +81,7 @@ setupStaticNetworking ()
     # broadcast address?
     #
     bcast='';
-    if [ ! -z "${broadcast}" ]; then
+    if [ -n "${broadcast}" ]; then
       bcast=" broadcast ${broadcast}"
     fi
 
diff --git a/hooks/common/90-make-fstab b/hooks/common/90-make-fstab
index 1f6757e..79be1ea 100755
--- a/hooks/common/90-make-fstab
+++ b/hooks/common/90-make-fstab
@@ -48,7 +48,7 @@ if [ "${ide}" ]; then
 elif [ "${scsi}" ]; then
     device=sda
 else
-    if [ ! -z "${disk_device}" ]; then
+    if [ -n "${disk_device}" ]; then
         device=`basename $disk_device`
     fi
 fi
diff --git a/hooks/gentoo/40-setup-networking b/hooks/gentoo/40-setup-networking
index bbb99ca..2c96654 100755
--- a/hooks/gentoo/40-setup-networking
+++ b/hooks/gentoo/40-setup-networking
@@ -61,7 +61,7 @@ setupStaticNetworking ()
     #  if $p2p is set then add a "pointopoint" setting.
     #
     point='';
-    if [ ! -z "${p2p}" ]; then
+    if [ -n "${p2p}" ]; then
         point="pointopoint ${p2p}"
     else
         point=''
diff --git a/misc/xen-tools.bash-completion b/misc/xen-tools.bash-completion
index 0a15e87..ac6fd53 100644
--- a/misc/xen-tools.bash-completion
+++ b/misc/xen-tools.bash-completion
@@ -31,7 +31,7 @@ function _find_xen_images
 
     for i in /etc/xen/*.cfg ; do
         name=`grep ^name $i 2>/dev/null | awk -F\'  '{print $2}'`
-        if [ ! -z "${name}" ] ; then
+        if [ -n "${name}" ] ; then
             names="${names} ${name}"
         fi
     done