Persistence can be defined as the continued or prolonged existence of something. Persistence plays an important role in computing. Random Access Memory (RAM) is fast and volatile, meaning its contents get erased when the system is powered off. However, we still recognize our computers when ever we login. This is the power of persistence in computing.
Persistence makes computing systems to have personality. You configure a system and it remembers these configurations till you decide to explicity change them. The major abstraction for persistence is the ‘file system’. Unlike the RAM, files stored on devices and are there to stay.
This ability to store files can be used to do real good, especially on Unix environments. Unix was originally known as the Programmer’s Work Bench (PWB), because of its ease of configuration and clean design. Programmer’s would customize their Unix environments in every possible way to derive a comfortable working environment.
Take the shell, also known as the terminal, for example. It can be used to perform file and directory manipulations among other versatile tasks. Navigating to the notes directory in the Documents folder can be done by the command:
cd ~/Documents/notes
Since laziness is a virtue, i won’t want to type ‘cd ~/Documents/notes’ every time. Unix being flexible and customizable provides a command just for people like me(and maybe you), the alias command.
/alias notes=’cd ~/Documents/notes’/
This would register notes to be a shortcut for the long cd ~/Documents/notes/ command. However, making alias entries in the terminal is not persistent. The registered aliases won’t work when the shell is restarted. A solution to this, as it is for many configurable systems, is to save the aliases in a configuration file. I have come to realize that providing configuration files is a popular and clean way of making programs and systems customizable by users, which is common to Unix applications such as emacs, vim, and the terminal.
Interestingly, to avoid the RAM effects on our settings, aliases in this case, we need to manipulate any of the 2 files listed below. Feel free to create these files in your home Unix home directory if they don’t exist:
What do these files do? Initialization is an important step in computational processes. When the terminal is started by a user, the system first looks for personal configurations in a series of files.
~/.bashprofile : has higher precedence.
Common settings to put in these files are environmental variable configurations, custom messages to print when the terminal starts, aliases etc
Moreover, to make our aliases persistent, we should save them in the ~/.bashprofile or ~/.bashrc files. I personally prefer ~/.bashrc because it easier to type. In this file, we can store our custom settings:
/alias notes=’cd ~/Documents/notes’/
Fun experiments with this file are:
As is the goal of data persistence, your settings will remain in the system till you need them no more. A variety of Unix applications use this config/settings file model to enable users to customize their enviroments:
In a nutshell, persistence is essential in data storage, personality, and customization.