Question

How to set environment variable in shell script?

Asked by: LuRen

hi,

I use redhat 7.3 (2.4.18). But i can't set environment variable
in shell script. please check my code:

=============test==========
#!/bin/bash
CLASSPATH=/usr/test
export CLASSPATH
============================

and in shell, i execute the commands:

# chmod +x test
# ./test

there is no error occured. but when i check use "#set", I can't
find CLASSPATH variable. What's the matter? How can i do?

any help will be very appreciated.

TIA.

-- lr

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Asked On
2003-06-12 at 20:37:23ID20646792
Tags

environment

,

script

,

set

,

variable

,

shell

Topic

Linux Setup

Participating Experts
2
Points
20
Comments
5

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Answers

 

by: jleviePosted on 2003-06-12 at 20:58:14ID: 8714635

The difficulty here is that env variables are only inherited from the parent shell. Your script is working correctly and in the shell that is executing the script and in any shells that the script might start the variable will exist. It won't, however, exist in the shell you use to execute the script.

If you want the variable to exist in your login shell you need to place the definition in the shell init script in your home directory (.bashrc, .cshrc, etc) or define it on the command line.

 

by: LuRenPosted on 2003-06-13 at 00:34:23ID: 8715521

>jlevie Wrote:

>The difficulty here is that env variables are only inherited from the parent shell. Your script is working correctly and in the shell >that is executing the script and in any shells that the script might start the variable will exist. It won't, however, exist in the >shell you use to execute the script.

  I still don't understand why it is. especially , "Your script is working correctly and *** in the shell that is executing the script and in any shells that the script might start the variable will exist. It won't, however, exist in the shell you use to execute the script.***"

>If you want the variable to exist in your login shell you need to place the definition in the shell init script in your home directory
>(.bashrc, .cshrc, etc) or define it on the command line.

   I have a try with rc (/etc/rc), but it seemed no useful.  i think rc will be executed when system startup.  but why the env variable, I set in the rc, is still not useful.  

    now i will have a try with .bashrc.  

    ----- lr

 

by: TheWeakestLinkPosted on 2003-06-13 at 01:33:44ID: 8715757

As the other posters have said, the problem is in the way variables are inherited.

However try this :-

I have a short bash script ............

#!/bin/bash
export TESTVAR=test

Doing what you suggest - just executing it measns that the variable testvar doesn't show up.

Now try "source ./testvar" and then look at env.  The new variable will be there in the calling shell.
If you only wnat to set variables, you don't need the #!/bin/bash part anyway.

Paul

 

by: jleviePosted on 2003-06-13 at 20:45:30ID: 8722416

Let me try a more detailed explanation.

And env var is a kev-value pair that is maintained and made available by a shell. The variable only exists while
that shell is running and it makes those variables available to any processes (including other shells) that are
started by that shell. So we speak of env variables being inherited by "children' of the shell that the variable was
exported from.  A variable defined and exported by a child process or shell isn't visible to the parent shell that
started said process or shell, inheritance only passes to the children.

When you log in there is a login shell that you interact with (a shell for a console login, telnet, rlogin,
or ssh session) or a parent process that starts your desktop. And env var that is exported by that login shell or
process will be available to that or it's children. Attempting to define an env var in one of the system init scripts
doesn't work because each of those is run from a shell started by the system and that shell exits when the it's
done its work, thus 'destroying' and env vars it has created while doing it's job.

The proper place to define an env var is in the global shell init scripts (/etc/profile for Bourne/Bash/Ksh or
/etc/csh.cshrc for Csh/Tcsh) or in the user's shell init scripts (~/.bashrc, ~./tchsrc, etc)

Or you can do as TheWeakestLink suggest and (for a bash shell) "source the file" containing the env var
definition. That works because it is the current shell that reads and executes the commands found in the file.

 

by: LuRenPosted on 2003-06-15 at 07:40:52ID: 8726981

jlevie, TheWeakestLink
   
         Thank you all very much.  I use the command "source ./test" and it works. and more, i use  the command ". ./test" , it works, too.

        thank jlevie especially  for your detailed explanation.  

        I think you should all get the points.      I'll post a question only TheWeakestLink to get the points.


       -- lr

 

20120131-EE-VQP-002

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