how i devaluate duplication constants?

i have perl book tangible constants settlement files. example:

use consistent  {
log_dir                             => "/var/log/",
log_filename                        => "/var/log/file1.log",
log4perl_conf_file                  => "/etc/app1/log4perl.conf",
conf_file1                          => "/etc/app1/config1.xml",
conf_file2                          => "/etc/app1/config2.xml",
conf_file3                          => "/etc/app1/config3.xml",
conf_file4                          => "/etc/app1/config4.xml",
conf_file5                          => "/etc/app1/config5.xml",
};

i wish devaluate duplication "/etc/app1" "/var/log" , nonetheless controlling variables does work. also controlling formerly tangible constants does work same "use consistent block". example:

use consistent {
log_dir                             => "/var/log/",
file_filename                       => log_dir . "file1.log" 
};

does work.

using removed "use constant" blocks does workaround problem, nonetheless adds lot unneeded code.

what repremand proceed this?

thank you.