[logback-user] Special Joran substitution

[Diego Louzán]

Ceki Gulcu escribió:
> Hello Diego,
> 
> The special syntax originates from Bash, at least that's where I saw it fist.
> 
> http://www.faqs.org/docs/abs/HTML/parameter-substitution.html
> http://tldp.org/LDP/abs/html/refcards.html#AEN20779
> http://www.purinchu.net/wp/2005/06/11/advanced-parameter-substitution-with-bash/
> 
> Thus, "${varnname:-word}" means, if varname exists and isn't null, return its 
> value, otherwise return 'word'.
> 
> If my memory serves me correctly, the special substitution syntax is needed 
> because, we would like to have the name of the parameter to vary with the 
> circumstances. More precisely, while most database drivers take expect the name 
> of the "url" parameter to be "url", some database drivers expect that the value 
> be passed using a different variable name.
> 
> Does this help?
> 
> Diego Louzán wrote:
>> In chapter4 of the documentation the following example is shown:
>>
>> <dataSource class="${dataSourceClass}">
>>      <!-- Joran cannot substitute variables
>>           that are not attribute values. Therefore, we cannot
>>           declare the next parameter like the others.
>>      -->
>>      <param name="${url-key:-url}" value="${url_value}"/>
>>      <serverName>${serverName}</serverName>
>>      <databaseName>${databaseName}</databaseName>
>> </dataSource>
>>
>> I can't figure out that special syntax for Joran in "${url-key:-url}", 
>> can anybody explain it to me? Why is it needed in that example?
>>
>> Regards.
>> Diego.

I'm not much of a bash fan, so no wonder I had never heard about that
syntax xD Thanks for clearing that up.

Regards.
Diego.