How compare current_setting(..) ?

Hi there,

I'd like to check that my log_line_prefix is set to '%t'.
I suppose I can check it with the following statement:   SELECT current_setting( 'log_line_prefix' )   WHERE
current_setting('log_line_prefix' ) != '%t'
 

But it returns every time a row, with '%t', even when log_line_prefix is set 
to '%t'.
What's wrong ?

TIA,
Sabin