MySQL Bugs: #69962: Allow postfix like variable reference in configuration file

Bug #69962	Allow postfix like variable reference in configuration file
Submitted:	8 Aug 2013 12:02
Reporter:	Arnaud Adant	Email Updates:
Status:	Verified	Impact on me:	None
Category:	MySQL Server: Options	Severity:	S4 (Feature request)
Version:		OS:	Any
Assigned to:		CPU Architecture:	Any

Description:
As the number of variables grows, it can be useful to define user variables that
can be assigned to configuration variables.

$temp = ./tmp
tmpdir = $tmp
innodb_temp_data_file_path = $tmp
slave_load_tmpdir = $tmp

see

http://www.postfix.org/BASIC_CONFIGURATION_README.html and this quote:

"You specify a configuration parameter as:

/etc/postfix/main.cf:
   parameter = value
and you use it by putting a "$" character in front of its name:

/etc/postfix/main.cf:
   other_parameter = $parameter
You can use $parameter before it is given a value (that is the second main difference with UNIX shell variables). The Postfix configuration language uses lazy evaluation, and does not look at a parameter value until it is needed at runtime.
"

see also http://bugs.mysql.com/bug.php?id=55705

How to repeat:
Feature request

For course $tmp and not $temp ! This would be an error on start up

$tmp = ./tmp
tmpdir = $tmp
innodb_temp_data_file_path = $tmp
slave_load_tmpdir = $tmp

You should not create temporary new variables, as that makes life more of a mess.
Just do the following which is much simpler:

tmpdir = ./tmp
innodb_temp_data_file_path = $tmpdir
slave_load_tmpdir = $tmpdir

Or if you are happy with the default value of tmpdir:

innodb_temp_data_file_path = $tmpdir
slave_load_tmpdir = $tmpdir