Why Should You Use Environment Variables? Some popular use cases include %CD% for the current directory and %TIME% for the current time. There is a fixed list of such variables, and you can use them in your code to make your job easier. While you can assign a value to an environment variable manually by using the SET command or its equivalent, you can not assign values to pseudo environment variables. These are not statically assigned pairs of keys and values, but rather dynamic references that return various values when queried. Environment Variables vs Pseudo-environment VariablesĪ separate line of dynamic environment variables is available in Windows and DOS-based systems, known as pseudo environment variables. ~/bashrc or ~.profile that are loaded when the system boots up. If you need to set some environment variables as default to be loaded each time any program runs on your system, you need to define them in files such as. In such systems, everything is stored under a var object and can be accessed/modified by the running program. Unlike Windows systems, Unix-based systems do not have three layers of environment variable types. Environment Variables in Unix-based Systems Runtime variables are usually not permanent unless scripted, and you need to define them whenever you start a new process. You can use terminal scripting to create and store these variables on the fly. These are usually set by the parent process that creates the new process and is accompanied by the system and user environment variables as well. Runtime environment variables are further narrowed down only to the runtime or the process that they are associated with. These variables are helpful when implementing local changes in your system without affecting other users. You do not need the system administrator to make changes to these variables you can do that yourself as a user. These variables are used to store user-specific information such as the path to a local installation of libraries that are not to be used by all users, values specific to programs installed only for specific users, etc. User environment variables are those that are local to a user profile in Windows systems. One of the most common uses of a system environment variable is setting up a PATH variable to a global package/library to be used by all users in the system. Your operating system/system administrator usually sets these, and you’re rarely required to fiddle with them. System environment variables reside on the topmost root of the system and are the same for all processes running in a system under all the user profiles of the system. There are three prominent types of environment variables in a Windows-based computer system, and each of them has its use cases.
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