I'm diving into Bash scripting and learning from resources like Linux Journey, but I'm a bit stuck on the concept of environment variables. As I understand it, environment variables are essentially variables that hold information. For example, the PATH variable indicates where the shell can find executable files for commands, while PWD tells me what my current directory is. I get that these variables can be temporarily altered using a command like "export PATH=/example" (which changes the path just for the current session), or permanently by modifying configuration files. They are set up when the shell starts (or when I open it, not sure).
However, I'm confused about why some variables, like PATH, are used to direct the shell to look for executable files, while others, like PWD, just provide information. I read that some variables are operational (like PATH) while others carry state information (like PWD). Can anyone confirm if I'm understanding this correctly? I'm really new to this and would appreciate any help!
4 Answers
Environment variables are indeed global variables for your shell session. Think of them as default parameters that shape how programs behave during their execution. While you can have temporary variables for local tasks in scripts, environment variables let applications know what settings to start with across different sessions. Just keep an eye on capitalizing them—that's the convention!
You're definitely on the right track! Think of environment variables as global variables accessible by applications running in your shell. Like a good program scope, they can be defined and accessed across processes. When you create one and export it, you're making it available to child processes of that shell. If you don't export it, it will just be a local variable for that instance. Variables in Bash behave a bit differently regarding scope—just keep that in mind as you go!
Exactly! And when you export a variable, you're essentially saying, 'Hey, other processes, you can use this variable too.' It’s a neat way to allow different scripts or commands to share information.
Your understanding isn't quite on point. Environment variables are not just simple variables; they essentially create blocks of memory used by every process in Linux. For instance, PATH tells the shell where to find command executables because the exec functions in libraries, like libc, are designed to look there when you try to run a command. On the other hand, PWD maintains the current working directory but isn't automatically updated in the same way—it relies on the shell to update it whenever you change directories. So, yes, one directs the shell where to look (PATH), while the other just holds info (PWD). Keep experimenting and asking questions, you'll get the hang of it!
Just to add, it's worth noting that you can technically name any variable anything you want for your scripts. Although, when it comes to standard scripts, they'll typically reference standard environment variables like PATH.
Right! And remember, every time you launch a new shell, it gets the environment variables from the parent process, which is why you see those variables pop up.
Here's a handy way to think about it: environment variables are like extra options or settings that influence the behavior of programs. They can act like command line arguments but are available globally. So, when you run an executable, it automatically receives these variables to help it run correctly. Plus, running commands like `ps e` can show you the environment variables alongside the running processes, which can be very insightful!
Amen to that! All your global variables should stick to uppercase—helps keep things organized and easy to identify.