diff --git a/build.py b/build.py
index 71f5274d..9e61d692 100644
--- a/build.py
+++ b/build.py
@@ -28,7 +28,7 @@ else:
         ("acorndfs", "", "--200"),
         ("agat", "", ""),
         ("amiga", "", ""),
-        ("apple2", "", "--140 40track_drive"),
+        ("apple2", "", "--140 -c 40track_drive"),
         ("atarist", "", "--360"),
         ("atarist", "", "--370"),
         ("atarist", "", "--400"),
@@ -38,17 +38,17 @@ else:
         ("atarist", "", "--800"),
         ("atarist", "", "--820"),
         ("bk", "", ""),
-        ("brother", "", "--120 40track_drive"),
+        ("brother", "", "--120 -c 40track_drive"),
         ("brother", "", "--240"),
         (
             "commodore",
             "scripts/commodore1541_test.textpb",
-            "--171 40track_drive",
+            "--171 -c 40track_drive",
         ),
         (
             "commodore",
             "scripts/commodore1541_test.textpb",
-            "--192 40track_drive",
+            "--192 -c 40track_drive",
         ),
         ("commodore", "", "--800"),
         ("commodore", "", "--1620"),
@@ -60,17 +60,17 @@ else:
         ("ibm", "", "--1232"),
         ("ibm", "", "--1440"),
         ("ibm", "", "--1680"),
-        ("ibm", "", "--180 40track_drive"),
-        ("ibm", "", "--160 40track_drive"),
-        ("ibm", "", "--320 40track_drive"),
-        ("ibm", "", "--360 40track_drive"),
+        ("ibm", "", "--180 -c 40track_drive"),
+        ("ibm", "", "--160 -c 40track_drive"),
+        ("ibm", "", "--320 -c 40track_drive"),
+        ("ibm", "", "--360 -c 40track_drive"),
         ("ibm", "", "--720_96"),
         ("ibm", "", "--720_135"),
         ("mac", "scripts/mac400_test.textpb", "--400"),
         ("mac", "scripts/mac800_test.textpb", "--800"),
         ("n88basic", "", ""),
         ("rx50", "", ""),
-        ("tartu", "", "--390 40track_drive"),
+        ("tartu", "", "--390 -c 40track_drive"),
         ("tartu", "", "--780"),
         ("tids990", "", ""),
         ("victor9k", "", "--612"),
diff --git a/lib/config/flags.cc b/lib/config/flags.cc
index bc54262a..f474673b 100644
--- a/lib/config/flags.cc
+++ b/lib/config/flags.cc
@@ -13,17 +13,23 @@ static std::vector<Flag*> all_flags;
 static std::map<const std::string, Flag*> flags_by_name;
 
 static void doHelp();
+static void doLoadConfig(const std::string& filename);
 static void doShowConfig();
 static void doDoc();
 
 static FlagGroup helpGroup;
 static ActionFlag helpFlag = ActionFlag({"--help"}, "Shows the help.", doHelp);
 
-static ActionFlag showConfigFlag = ActionFlag({"--config", "-C"},
+static FlagGroup configGroup;
+static ActionFlag loadConfigFlag({"--config", "-c"},
+    "Reads an internal or external configuration file.",
+    doLoadConfig);
+
+static ActionFlag showConfigFlag({"--show-config", "-C"},
     "Shows the currently set configuration and halts.",
     doShowConfig);
 
-static ActionFlag docFlag = ActionFlag(
+static ActionFlag docFlag(
     {"--doc"}, "Shows the available configuration options and halts.", doDoc);
 
 FlagGroup::FlagGroup()
@@ -182,17 +188,16 @@ void FlagGroup::parseFlags(int argc,
             "non-option parameter '{}' seen (try --help)", *filenames.begin());
 }
 
+static void doLoadConfig(const std::string& filename)
+{
+    globalConfig().readBaseConfigFile(filename);
+}
+
 void FlagGroup::parseFlagsWithConfigFiles(int argc,
     const char* argv[],
     const std::map<std::string, const ConfigProto*>& configFiles)
 {
-    parseFlags(argc,
-        argv,
-        [&](const auto& filename)
-        {
-            globalConfig().readBaseConfigFile(filename);
-            return true;
-        });
+    FlagGroup({this, &configGroup}).parseFlags(argc, argv);
 }
 
 void FlagGroup::checkInitialised() const
diff --git a/lib/config/flags.h b/lib/config/flags.h
index 67be675f..d8b96af4 100644
--- a/lib/config/flags.h
+++ b/lib/config/flags.h
@@ -83,13 +83,23 @@ public:
         const std::string helptext,
         std::function<void(void)> callback):
         Flag(names, helptext),
-        _callback(callback)
+        _voidCallback(callback),
+        _hasArgument(false)
+    {
+    }
+
+    ActionFlag(const std::vector<std::string>& names,
+        const std::string helptext,
+        std::function<void(const std::string&)> callback):
+        Flag(names, helptext),
+        _callback(callback),
+        _hasArgument(true)
     {
     }
 
     bool hasArgument() const override
     {
-        return false;
+        return _hasArgument;
     }
 
     const std::string defaultValueAsString() const override
@@ -99,11 +109,16 @@ public:
 
     void set(const std::string& value) override
     {
-        _callback();
+        if (_hasArgument)
+            _callback(value);
+        else
+            _voidCallback();
     }
 
 private:
-    const std::function<void(void)> _callback;
+    const std::function<void(const std::string&)> _callback;
+    const std::function<void(void)> _voidCallback;
+    bool _hasArgument;
 };
 
 class SettableFlag : public Flag
diff --git a/scripts/encodedecodetest.sh b/scripts/encodedecodetest.sh
index 80842e24..d8cbf5b9 100755
--- a/scripts/encodedecodetest.sh
+++ b/scripts/encodedecodetest.sh
@@ -14,10 +14,10 @@ destfile=$dir/dest.img
 
 dd if=/dev/urandom of=$srcfile bs=1048576 count=2 2>&1
 
-echo $fluxengine write $format -i $srcfile -d $fluxfile --drive.rotational_period_ms=200 $flags
-$fluxengine write $format -i $srcfile -d $fluxfile --drive.rotational_period_ms=200 $flags
-echo $fluxengine read $format -s $fluxfile -o $destfile --drive.rotational_period_ms=200 $flags
-$fluxengine read $format -s $fluxfile -o $destfile --drive.rotational_period_ms=200 $flags
+echo $fluxengine write -c $format -i $srcfile -d $fluxfile --drive.rotational_period_ms=200 $flags
+$fluxengine write -c $format -i $srcfile -d $fluxfile --drive.rotational_period_ms=200 $flags
+echo $fluxengine read -c $format -s $fluxfile -o $destfile --drive.rotational_period_ms=200 $flags
+$fluxengine read -c $format -s $fluxfile -o $destfile --drive.rotational_period_ms=200 $flags
 if [ ! -s $destfile ]; then
 	echo "Zero length output file!" >&2
 	exit 1