Shell Programming and Scripting

I have a master shell, which calls another shell to export some env variables. But when I just run the child shell from the command line, and see if the variables are exported by doing,

echo $EXPORTED_VAR1

I am not seeing the value.

But I am sure, I am using the child shell from a master shell which is running successfully daily.

What am I missing here. Purpose of my test is, I just added few more variables to be exported in the same script, just want to make sure if they are being exported OK.

Thx,

srishan

The master script exports variables. Then script it runs will see the new environment. But when the master script exits, its environment goes away. Now you're back to the original environment. A child process cannot affect the environment of its parent.

It is exactly the other way round.

Like I said in the first posting, Child is setting the env variables, Master calls child script to set up the env variables, which are then used by the master script through out. As per your explanation, once the child process finishes, the environment is gone, which does not seem right, as they are visible in the master script.

I do not know if I am explaining it right.

My doubt is, when I test it like the following, it does not show me any results.

Unix Prompt:> ksh child_process.ksh -- supposed to set the env
Unix Prompt:> echo $VAR1

-- Result is NULL here, although that variable has been set and exported in the child_process.ksh, why?

When the same script is executed from Master script, $VAR1 is available with it's value.

I am just trying to understand, how this exporting mechanism is working. Hope it is clear now.

Thx,

srishan

You are not seeing the environment variables because things really do work the way I said they do. Your login shell spawns a ksh process which executes youe script. This does change the environment of the ksh process. But it has no effect at all on the ebvironment of the login shell. Then the ksh process exits. Now you're back to the unchanged environment of the login shell.

Somewhere you've made an error if you think otherwise. The most probable explanation is that "I have a master shell, which calls another shell to export some env variables" is wrong. ksh has a concept of a "dotted script". If a script is invoked like this:
. /path/to/script
it works differently. Rather than invoking a new shell, the current shell just switches its own input to the script and starts processing. When it hits end of file, it continues after the dotted command. Since no child process was spawned, the current shell can change its own environment. This is my guess as to what's happening.

That is exactly what is going on.

The point that I was missing was the shell invokation,
. /child_shell vs /child_shell

Thanks,

srishan