Environment variable

Environment variable

An environment variable is a dynamic-named value that can affect the way running processes will behave on a computer. They are part of the environment in which a process runs. Environment variables are used by the operating system and by various applications to store configuration settings and other information.

Overview

Environment variables are a set of dynamic values that can influence the behavior of running processes on a computer. They are used to pass information into processes that are spawned from the shell or other programs. These variables can be used to store system-wide values, such as the location of system directories, or user-specific values, such as the user's home directory.

Common Environment Variables

Some of the most commonly used environment variables include:

• PATH: Specifies the directories in which executable programs are located.
• HOME: Indicates the current user's home directory.
• USER: Contains the name of the current user.
• SHELL: Specifies the path to the current user's shell.
• TEMP: Points to the directory where temporary files are stored.

Setting Environment Variables

Environment variables can be set in various ways, depending on the operating system and the shell being used. In Unix-like systems, environment variables can be set using the `export` command in Bash or the `setenv` command in csh and tcsh. In Microsoft Windows, environment variables can be set using the `set` command in the Command Prompt or through the System Properties dialog.

Accessing Environment Variables

Environment variables can be accessed by programs and scripts to retrieve configuration settings and other information. In many programming languages, there are built-in functions or libraries to access environment variables. For example, in Python, the `os` module provides the `os.environ` dictionary to access environment variables.

Security Considerations

Environment variables can sometimes contain sensitive information, such as passwords or API keys. It is important to handle them securely and avoid exposing them to unauthorized users. In some cases, environment variables can be used to inject malicious code into a system, so it is crucial to validate and sanitize their values.

Related Pages

• Operating system
• Shell (computing)
• Configuration file
• System directory
• User profile

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