That's an excellent question! You're really thinking deeply about these commands.
The export command in Linux (and Unix-like systems) is used to mark a variable as an environment variable.
Let me break down why that's important:
-
Local Variables vs. Environment Variables:
- When you create a variable like
flower=rose, it's a local variable (or shell variable). It only exists within the current shell session. Any new processes or shells you start from this current shell will not automatically know aboutflower. - When you use
export nut=almond, you are telling the shell: "Makenutan environment variable. Not only should it be available in this current shell, but also in any child processes or sub-shells that I start from here."
- When you create a variable like
-
Child Processes: Imagine your shell (where you are typing commands) is a parent. When you run another program (like
grep,ls,python, or even another shell script), that program becomes a "child process" of your current shell.- Local variables are not automatically passed down to these children.
- Environment variables are automatically passed down to these children. This is crucial for many programs that rely on environment settings to configure their behavior (e.g.,
PATH,HOME,JAVA_HOME).
So, in simple terms, export extends the visibility of a variable beyond the current shell to any processes that are started from it.
You've already seen this in action in the lab! You created flower (local) and nut (exported, so environment variable):
env | grep flowershowed no output, becausefloweris local to your current shell.env | grep nutdid show output, becausenutwas exported and is now an environment variable, visible toenv(which runs as a child process).
Does that explanation clarify the purpose of export for you?
