scripts: factor out benchmarks and run further with ./eeval and common_bench_cmd

eeval

@@ -1,4 +1,20 @@
 #!/usr/bin/env bash
+# echo and eval
+a=
+while getopts a OPT; do
+  case "$OPT" in
+    a)
+      # Append to file instead of overwriting.
+      a=-a
+      ;;
+    ?)
+      exit 2
+      ;;
+  esac
+done
+shift "$(($OPTIND - 1))"
 cmd="$1"
-echo "$cmd" | tee -a "${2:-/dev/null}"
+outfile="${2:-/dev/null}"
+echo "$cmd" | tee $a "$outfile"
 eval "$cmd"
+exit "$?"