improve command-line option handling

runcron.c

@@ -28,9 +28,39 @@ char *lock_dir = "/var/tmp";
 
 int usage() {
   fprintf(stderr,
+          "%s v%s - a cron job wrapper\n"
           "Usage: %s [<OPTIONS>] <COMMAND> [<ARGS>...]\n"
-          "%s v%s - a cron job wrapper\n",
-          PACKAGE, PACKAGE, PACKAGE_VERSION
+          "\n"
+          "Known options:\n"
+          "\n"
+          "   --help            Show this help message\n"
+          "   --splay SECONDS   Wait a random amount of time between 0 and SECONDS before\n"
+          "                     actually starting the command.\n"
+          "   --timeout SECONDS\n"
+          "                     If the command runs for more than the specified amount of\n"
+          "                     time, terminate it. By default commands can run forever.\n"
+          "\n"
+          "Options controlling the command output:\n"
+          "\n"
+          "   --quiet           Only show output from the command if it fails, suppress\n"
+          "                     all output if the exit status is 0.\n"
+          "   --syslog          Log command output to syslog, instead of stderr.\n"
+          "\n"
+          "Options controlling locking behavior:\n"
+          "\n"
+          "   -n, --name NAME   Set the job name. By default, the basename of COMMAND will\n"
+          "                     be used.\n"
+          "   --no-lock         Disable locking, allow running multiple instances at once.\n"
+          "   --wait            Wait for the lock to be released. If another instance of\n"
+          "                     this command is running, wait until it terminates (or\n"
+          "                     until the lock timeout expires).\n"
+          "   --lock-timeout SECONDS\n"
+          "                     Wait at most the specified amount of time for the instance\n"
+          "                     lock to be released, failing with an error if after SECONDS\n"
+          "                     the lock could not be obtained. If set to 0 (the default),\n"
+          "                     wait forever. Specifying this option implies --wait.\n"
+          "\n",
+          PACKAGE, PACKAGE_VERSION, PACKAGE
           );
   return 2;
 }
@@ -298,6 +328,22 @@ int main(int argc, char **argv) {
     }
   }
 
+  /* Check for option consistency. */
+  if (!locking) {
+    if (lock_wait) {
+      fprintf(stderr, "Error: --wait and --no-lock should not be specified together\n");
+      exit(2);
+    }
+    if (lock_timeout > 0) {
+      fprintf(stderr, "Error: --no-lock and --lock-timeout should not be specified together\n");
+      exit(2);
+    }
+  } else {
+    if (lock_timeout > 0) {
+      lock_wait = 1;
+    }
+  }
+
   if (optind >= argc) {
     fprintf(stderr, "Error: no command specified\n");
     exit(2);