diff --git a/releng/run_all_auto b/releng/run_all_auto
index 0b488697..dc483050 100755
--- a/releng/run_all_auto
+++ b/releng/run_all_auto
@@ -9,6 +9,7 @@ set -e
 SELF=$(basename "$0")
 GEN_DATA_DIR=releng_generated_data
 CLOG=${GEN_DATA_DIR}/log.${SELF}
+CLOG_PREV=${CLOG}.prev
 PASSED_OPTIONS="$@"
 RELENG_XORRISO=
 CLEANUP_LOG=0
@@ -62,7 +63,8 @@ cat << HLP
 
 ${SELF} runs executables from releng directory starting with auto_*,
 and passing them its own options. stdout/stderr output is stored in:
-./${CLOG}
+./${CLOG} (last run) and
+./${CLOG_PREV} (previous run)
 
 Usage: ${SELF} -x path/to/xorriso [-k] [-c] [-h]
    -x  absolute or relative path to xorriso binary to be run.
@@ -119,7 +121,7 @@ fi
 
 ########################################################
  if [ -f "${CLOG}" ]; then
-   mv "${CLOG}" "${CLOG}".prev
+   mv "${CLOG}" "${CLOG_PREV}"
  fi
  > ${CLOG}
  if [ -x "${RELENG_XORRISO}" ]; then
@@ -184,10 +186,10 @@ fi
          echo # | tee -a ${CLOG}
          echo -n "${SELF}: Removed my own log ${CLOG}." # | tee -a ${CLOG}
       fi
-      if [ -f "${CLOG}".prev ]; then
-         rm -f "${CLOG}".prev
+      if [ -f "${CLOG_PREV}" ]; then
+         rm -f "${CLOG_PREV}"
          echo # | tee -a ${CLOG}
-         echo "${SELF}: Removed my own log ${CLOG}.prev." # | tee -a ${CLOG}
+         echo "${SELF}: Removed my own log ${CLOG_PREV}." # | tee -a ${CLOG}
       fi
  else
       E2=`date '+%s'`
@@ -231,9 +233,9 @@ fi
       echo "~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~" | tee -a ${CLOG}
 
       ##### TODO: work out a less noisy diff'ing technique!
-      if [ -f "${CLOG}".prev -a -f "${CLOG}" ]; then
+      if [ -f "${CLOG_PREV}" -a -f "${CLOG}" ]; then
         echo "${SELF}: See diff against previous log file (might be long):" | tee -a ${CLOG}
-	echo "diff -Naur ${CLOG}.prev ${CLOG} | less" | tee -a ${CLOG}
+	echo "diff -Naur ${CLOG_PREV} ${CLOG} | less" | tee -a ${CLOG}
       fi
 
  fi