All Configuration Files are Plain Text

Plain Text Configs?

Almost all of the configuration files in a Linux system are text files under /etc. You get the odd application that stores it’s config in a binary format like a SQL database, specialized or some other proprietary format.

The benefit of text, however, is the ease of accessing it. You don’t need to implement an API, which if it’s your first implementation can set you back quite some time. And if you only need 1 or 2 entries from it, could end up as a huge expense. Having the configuration available as plain text you can immediately access it with the myriad of stream processors you have at your disposal, like grep, sed, awk, cut, cat, sort to name a few, or inside programming languages any of the file operations and methods.

To give an example, lets say I wanted to know the PIDs of all the users on the system. I didn’t need their names, just the PIDs, it’s as simple as this (assuming you don’t use something like NIS):

awk -F ':' '{print $3}' /etc/passwd

Or if you wanted to get a list of all hostnames a specified IP is associated with in /etc/hosts:

grep "127.0.0.1" hosts | cut -f 2- -d ' '

A very useful one is where your configuration file’s entries take the format of

RUN_DAEMON="true"
INTERFACE="127.0.0.1"
PORT="7634"

In this case you can easily extract the values from the file. For example, if the configuration file is named /etc/default/hddtemp, and you want to extract the PORT option, you simply need to do:

value=$( . "/etc/default/hddtemp"; echo $PORT )
echo "PORT has value: $value"

Or for the same file, if you want to extract those options into your current environment, it’s as simple as doing:

. "/etc/default/hddtemp"
echo "PORT has value: $PORT"
echo "INTERFACE has value: $INTERFACE"

What the above does is evaluate the configuration file as a bash script, which then basically sets those configuration options as variables (since they use the same syntax as bash for setting variables). The difference between the first and the second method, is that the second method could potentially override variables you’re already using in your environment/script (imagine already using a variable named PORT at the time of loading the configuration file). The first method loads the configuration in it’s own environment and only returns the value you requested.

Note that when using these 2 methods, had there been commands in the configuration files they would have been executed. So be aware of this if you decide to use this technique to read your configuration files. It’s very useful, but unless you’re careful you could end up with security problems.

Conclusion

The mere fact that these files are text means you immediately have access to it using methods available to even the most primitive scripting/programming langauges, and all existing text capable commands and programs are able to view/edit your configuration files.

Something like the Windows registry surely has it’s benefits. But in the world of Unix pipes/fifos, having it all text based is a definite plus.

So Why Love Linux? Because it has mostly plain text configuration files.