macdown-cmd.mm

if (argc < 2)
{
    // Launch normally.
    return;
}
NSString *path = [NSString stringWithUTF8String:argv[1]];
path = [path stringByStandardizingPath];    // You should do this, BTW.
if ([[NSFileManager defaultManager] fileExistsAtPath:path])
{
    // Open the file.
    return;
}

NSWorkspace *workspace = [NSWorkspace sharedWorkspace];
NSURL *appURL = [workspace URLForApplicationWithBundleIdentifier:@"com.uranusjr.macdown"];
NSDictionary *configuration = @{
    NSWorkspaceLaunchConfigurationArguments: @[
        @"-defaultSavePath", path,
    ],
};
[workspace launchApplicationAtURL:appURL
                          options:NSWorkspaceLaunchDefault 
                    configuration:configuration
                            error:NULL];    // Fallback to normal launch on error?