关于外壳变量和环境变量

Question

I'm reading Wrox, Beginning Linux Programming. But I've got a question about shell variables.

Here is a shell script named test.sh:

#! /bin/bash
read test
echo $test
exit 0

Then I chmod the script:

$ chmod +x test.sh
$ ./test,sh

When I type "ok", it echos the "ok".

But when I returned to the shell interface, I typed:

$ echo $test

It returned nothing...

I don't know why $test doesn't return "ok" just like the script does... And the book doesn't metion it...

Thanks in advance:)

Answer 1

The variables only exist in the process where they were created (and also in child processes, if they are exported). Running a script creates a new process, after the script ends, all its variables are lost.

You can run the script without starting a new process by "sourcing" it:

. ./test.sh

You should remove the exit then, though, otherwise it will exit your current shell.

Answer 2

It is because they are different processess, to "include" source of other script run

. test.sh

the test.sh should be without exit:

#! /bin/bash
read test
echo $test

Answer 3

Process locality

The values of environment variables are local, which means they are specific to the running process in or for which they were set. This means that if we open two terminal windows (which means we have two separate bash processes running), and change a value of an environment variable in one of the windows, that change will not be seen by the shell in the other window or any other program currently on the desktop.

For your more understanding : https://help.ubuntu.com/community/EnvironmentVariables