#342 fShadowEnvironment does not allow for optional variables (which can be empty)

[Jan Vogelgesang]

Unfortunately fShadowEnvironment doesn't go nice together with fAllowEmptyVars.
Here is the case. My config file contains the line:

appender.applog.File=${ProgramData}\${logname}-${USERNAME}${optionalSuffix}.log

So I have both Environment Variables and my custom variables which I set in the code.

• ${OptionalSuffix} is added only if app is run from command line, otherwise I would like to have it empy.
• ${UserName} I set manually in the code only when app is run as a services.
• ${logname} is my log name set in the code
• ${ProgramData} is an environment variable I don't touch in the code

I have 3 options:

1. use fShadowEnvironment

   Then I will have correctly resolved all variables but when ${optionalSuffix} is empty then I will end up with the log name: C:\ProgramData\MyLogName-janekvogel${optionalSuffix}.log

2. fAllowEmptyVars
   It will try to read every thing from System (will skip all custom variables).

3. fShadowEnvironment | fAllowEmptyVars
   Which also doesn't work. As it will never read system variables.

I think the best approach would be just to remove the not resolved property. So in fShadowEnvironment ${optionalSuffix} should be replaced with empty string if optionalSuffix is found neither in properties nor in system variables.

            else
               // Nothing has been subtituted, just move beyond the
                // unexpanded variable.
               // TODO: replace unresolved property with empty string
               i = var_end + DELIM_STOP_LEN;

       if (shadow_env)
                replacement = props.getProperty (key);
            if (! shadow_env || (! empty_vars && replacement.empty ()))
                internal::get_env_var (replacement, key);

            if (empty_vars || ! replacement.empty ())
            {
                // Substitute the variable with its value in place.
                pattern.replace (var_start, var_end - var_start + DELIM_STOP_LEN,
                    replacement);
                changed = true;
                if (rec_exp)
                    // Retry expansion on the same spot.
                    continue;
                else
                    // Move beyond the just substituted part.
                    i = var_start + replacement.size ();
            }
            else
               // Nothing has been subtituted, just move beyond the
                // unexpanded variable.
                i = var_end + DELIM_STOP_LEN;

[Jan Vogelgesang]

I think the code should be changed to something like:

            bool propertyExist = props.exists(key);
            if (propertyExist)
            {
                replacement = props.getProperty(key);
            }

            // if shadowing is not allowed or a property was not registered then try to look up in envrionment variables
            if (!shadow_env || !propertyExist)  
            {
                internal::get_env_var(replacement, key); 
            }

            // if empty values allowed or value is not empty then perform remplacement 
            if (empty_vars || !replacement.empty ())
            {
                ....