Configuration File Basics

Most programs in this suite use a common set of routines to read and interrogate configuration files. These configuration files contain named variables and their corresponding values. The routines then provide various ways of interpreting the value.

Files contains lines which are either comments, or variable names and their corresponding values.

Comments are assumed to be lines which start with '#'. Vaiables are any sequence of alpha-numerics ( plus '_', '.', '-' ) followed by a comma, space or equals symbol. The remainder of the line (starting from the next alpha-numeric) is assumed to be the value associated with that variable.

Programs which use the configuration system enquire of the value associated with a variable. There are then routines which will interpret the value and return the result.

A value can be interpreted as:

a string
a flag
a integer
a floating point number
a dynamic string

There now follows a more detailed description of these types.

A String

This is simply a string of characters, exactly as stored by the configuration system. Any structure that is required must be applied by the calling program.

An example would be:

    MY_NAME=Michael Caine

A Flag

The value associated with the variable is checked and if it is TRUE, or ON, or YES then the value 1 is returned to the calling program. If the variable value is not one of the above, or the variable does not exist, then the value 0 is returned to the calling program.

    SCREAM_AT_MONSTER=YES

An Integer

The value associated with the variable is converted to an integer which is returned to the calling routine. If the variable does not exist, or the value is not numeric, then the value returned to the calling program is 0.

    NUMBER_OF_PROGRAMMERS_TO_CHANGE_LIGHT_BULB=5

A Floating Point Number

The value associated with the variable is converted to an floating point number which is returned to the calling routine. If the variable does not exist, or the value is not numeric, then the value returned to the calling program is 0.0 .

    PI=3.14159265

A Dynamic String

The value associated with the variable is evaluated as if it were a shell variable. For example, if the configuration system contains

    LOGFILE=$HOME/logfile

and the environment has

    HOME=/home/me

the result of evaluating LOGFILE would be /home/me/logfile.

There are a couple of other variations which are associated with dynamic evaluation.

If the value contains a '%' character, the following word is treated as a configuration variable, and the value associated with the variable is used in place of the variable.
If the original variable is not found, a NULL string is returned, unless a default string is supplied, in which case that is evaluated as if it were the value associated with the variable.

To illustrate;
If the configuration file contains:

    FORENAME=Leonardo
    SURNAME=Da Vinci
    TITLE=Mr.
    FULL_NAME=%TITLE %FORENAME %SURNAME

and the environment has

    HOME=/home/me

Then the results of evaluation are:

    VARIABLE	DEFAULT			RESULT

    FULL_NAME	NULL			Mr. Leonardo Da Vinci
    LOGFILE	NULL			NULL
    LOGFILE	$HOME/logfile.%FORENAME	/home/me/logfile.Leonardo