diff --git a/share/man/man5/periodic.conf.5 b/share/man/man5/periodic.conf.5
--- a/share/man/man5/periodic.conf.5
+++ b/share/man/man5/periodic.conf.5
@@ -23,7 +23,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd March 9, 2022
+.Dd December 4, 2023
 .Dt PERIODIC.CONF 5
 .Os
 .Sh NAME
@@ -639,6 +639,13 @@
 Set to a list of extra scripts that should be run after all other
 daily scripts.
 All scripts must be absolute path names.
+.It Va daily_diff_flags
+.Pq Vt str
+Set to the arguments to pass to the
+.Xr diff 1
+utility when generating differences.
+The default is
+.Fl b u .
 .El
 .Pp
 The following variables are used by the standard scripts that reside in
diff --git a/usr.sbin/periodic/etc/daily/200.backup-passwd b/usr.sbin/periodic/etc/daily/200.backup-passwd
--- a/usr.sbin/periodic/etc/daily/200.backup-passwd
+++ b/usr.sbin/periodic/etc/daily/200.backup-passwd
@@ -40,7 +40,7 @@
 	    then
 		[ $rc -lt 1 ] && rc=1
 		echo "$host passwd diffs:"
-		diff -uI '^#' $bak/master.passwd.bak /etc/master.passwd |\
+		diff ${daily_diff_flags} -I '^#' $bak/master.passwd.bak /etc/master.passwd |\
 			sed 's/^\([-+ ][^:]*\):[^:]*:/\1:(password):/'
 		mv $bak/master.passwd.bak $bak/master.passwd.bak2
 		cp -p /etc/master.passwd $bak/master.passwd.bak || rc=3
@@ -57,7 +57,7 @@
 	    then
 		[ $rc -lt 1 ] && rc=1
 		echo "$host group diffs:"
-		diff -u $bak/group.bak /etc/group
+		diff ${daily_diff_flags} $bak/group.bak /etc/group
 		mv $bak/group.bak $bak/group.bak2
 		cp -p /etc/group $bak/group.bak || rc=3
 	    fi
diff --git a/usr.sbin/periodic/etc/daily/210.backup-aliases b/usr.sbin/periodic/etc/daily/210.backup-aliases
--- a/usr.sbin/periodic/etc/daily/210.backup-aliases
+++ b/usr.sbin/periodic/etc/daily/210.backup-aliases
@@ -34,7 +34,7 @@
 	    then
 		[ $rc -lt 1 ] && rc=1
 		echo "$host aliases diffs:"
-		diff -u $bak/aliases.bak /etc/mail/aliases
+		diff ${daily_diff_flags} $bak/aliases.bak /etc/mail/aliases
 		mv $bak/aliases.bak $bak/aliases.bak2
 		cp -p /etc/mail/aliases $bak/aliases.bak || rc=3
 	    fi
diff --git a/usr.sbin/periodic/etc/daily/221.backup-gpart b/usr.sbin/periodic/etc/daily/221.backup-gpart
--- a/usr.sbin/periodic/etc/daily/221.backup-gpart
+++ b/usr.sbin/periodic/etc/daily/221.backup-gpart
@@ -27,7 +27,7 @@
 			rm "${file}.tmp"
 		else
 			rc=1
-			[ -n "$show_diff" ] && diff "${file}.bak" "${file}.tmp"
+			[ -n "$show_diff" ] && diff ${daily_diff_flags} "${file}.bak" "${file}.tmp"
 			mv "${file}.bak" "${file}.bak2" || rc=3
 			mv "${file}.tmp" "${file}.bak" || rc=3
 		fi
diff --git a/usr.sbin/periodic/etc/daily/222.backup-gmirror b/usr.sbin/periodic/etc/daily/222.backup-gmirror
--- a/usr.sbin/periodic/etc/daily/222.backup-gmirror
+++ b/usr.sbin/periodic/etc/daily/222.backup-gmirror
@@ -25,7 +25,7 @@
 			rm "${file}.tmp"
 		else
 			rc=1
-			[ -n "$show_diff" ] && diff "${file}.bak" "${file}.tmp"
+			[ -n "$show_diff" ] && diff ${daily_diff_flags} "${file}.bak" "${file}.tmp"
 			mv "${file}.bak" "${file}.bak2" || rc=3
 			mv "${file}.tmp" "${file}.bak" || rc=3
 		fi
diff --git a/usr.sbin/periodic/etc/daily/223.backup-zfs b/usr.sbin/periodic/etc/daily/223.backup-zfs
--- a/usr.sbin/periodic/etc/daily/223.backup-zfs
+++ b/usr.sbin/periodic/etc/daily/223.backup-zfs
@@ -25,7 +25,7 @@
 			rm "${file}.tmp"
 		else
 			rc=1
-			[ -n "$show_diff" ] && diff "${file}.bak" "${file}.tmp"
+			[ -n "$show_diff" ] && diff ${daily_diff_flags} "${file}.bak" "${file}.tmp"
 			mv "${file}.bak" "${file}.bak2" || rc=3
 			mv "${file}.tmp" "${file}.bak" || rc=3
 		fi
diff --git a/usr.sbin/periodic/periodic.conf b/usr.sbin/periodic/periodic.conf
--- a/usr.sbin/periodic/periodic.conf
+++ b/usr.sbin/periodic/periodic.conf
@@ -31,6 +31,7 @@
 # that output.  $daily_output might be set to /var/log/daily.log if you
 # wish to log the daily output and have the files rotated by newsyslog(8)
 #
+daily_diff_flags="-u"				# flags for diff output
 daily_output="root"					# user or /file
 daily_show_success="YES"				# scripts returning 0
 daily_show_info="YES"					# scripts returning 1