diff --git a/dahdi-bash-completion b/dahdi-bash-completion
index d98074a..b93059a 100644
--- a/dahdi-bash-completion
+++ b/dahdi-bash-completion
@@ -48,7 +48,7 @@ __dahdi_span_types() {
 	has_cmd=0
 	for (( i=0; i < COMP_CWORD; i++)); do
 		case "${COMP_WORDS[$i]}" in
-		dumpconfig | list | set)
+		dumpconfig | list | set | compare)
 			has_cmd=1
 			break
 			;;
@@ -69,7 +69,7 @@ __dahdi_span_types() {
 					grep -l '[EJT]1' /sys/devices/pci0000:00/0000:00:10.4/usb1/1-1/xbus-00/*/spantype 2>/dev/null | sed -e 's|/spantype||') )
 			else
 				COMPREPLY=( ${COMPREPLY[@]} $(compgen -W \
-					'dumpconfig list set' -- $cur) )
+					'dumpconfig list set compare' -- $cur) )
 			fi
 			;;
 		esac
diff --git a/dahdi_span_types b/dahdi_span_types
index 4154772..5fce110 100755
--- a/dahdi_span_types
+++ b/dahdi_span_types
@@ -69,6 +69,7 @@ usage() {
 	echo >&2 "Usage: $0 [options] action [devpath ...]"
 	echo >&2 "       action:"
 	echo >&2 "         set        - set spans to E1/T1 according to /etc/dahdi/span-types.conf"
+	echo >&2 "         compare    - show config values that differ from system"
 	echo >&2 "         list       - human-readable list of all spans"
 	echo >&2 "         dumpconfig - dump current state in /etc/dahdi/span-types.conf format"
 	echo >&2 ""
@@ -88,6 +89,8 @@ if [ $? != 0 ]; then
 	usage
 fi
 
+compare=false
+
 # Note the quotes around `$TEMP': they are essential!
 eval set -- "$TEMP"
 
@@ -321,13 +324,26 @@ handle_span() {
 					echo >&2 "Set $devname span $spanno = $val"
 				fi
 				if [ "$dry_run" != 'true' ]; then
-					echo "$spanno:$val" > "$attr_file"
+					if [ "$compare" = 'true' ]; then
+						config="$spanno:$val"
+						system=`grep "$spanno:" "$attr_file"`
+						if [ "$config" != "$system" ]; then
+
+							active_val=`echo $system | cut -d: -f2`
+							echo "$devname $spanno     $val     $active_val" >>"$compare_results_file"
+						fi
+					else
+						echo "$spanno:$val" > "$attr_file"
+					fi
 				fi
 			fi
 		done
 }
 
 set_all_devices() {
+	span_differs='false'
+	SPANS_DIFFER='false'
+
 	if [ ! -f "$DAHDISPANTYPESCONF" ]; then
 		echo >&2 "$0: Missing configuration '$DAHDISPANTYPESCONF'"
 		exit 1
@@ -348,6 +364,16 @@ set_all_devices() {
 			esac
 		done
 	done
+	if [ "$compare" = 'true' ]; then
+		if [ -s "$compare_results_file" ]; then
+			echo "# Device           Unit  Config Active"
+			cat "$compare_results_file"
+			rm -f "$compare_results_file"
+			exit 5
+		fi
+		rm -f "$compare_results_file"
+		exit 0
+	fi
 }
 
 case "$action" in
@@ -360,6 +386,11 @@ dumpconfig)
 set)
 	set_all_devices
 	;;
+compare)
+	compare=true
+	compare_results_file=`mktemp`
+	set_all_devices
+	;;
 *)
 	usage
 	;;
diff --git a/doc/dahdi_span_types.8 b/doc/dahdi_span_types.8
index 4aba1a9..2bdd9ed 100644
--- a/doc/dahdi_span_types.8
+++ b/doc/dahdi_span_types.8
@@ -4,7 +4,7 @@
 dahdi_span_types \- set line modes of DAHDI spans before assignment
 .SH SYNOPSIS
 
-.B dahdi_span_types [\fIoptions\fB] <list|dumpconfig|set> \fB[\fIdevpath \fB...]
+.B dahdi_span_types [\fIoptions\fB] <list|dumpconfig|compare|set> \fB[\fIdevpath \fB...]
 
 .SH DESCRIPTION
 The span type (the line mode: E1/T1/J1) must be set to a span before
@@ -58,6 +58,16 @@ device(s) specified in the command line (or all devices, if none
 specified).
 .RE
 
+.B compare
+.RS
+Compare the settings on the system to those in the configuration file.
+For each line that applies to a device on the system, print it if the
+value to be set and the active value on the system differ.
+
+The exit status is 0 if there is no difference and non-zero if a
+difference was detected.
+.RE
+
 .B list
 .RS
 List line modes for all spans in the system which may be set with