Shell Scripting doubt

varunisac · 12-02-2010, 06:35 AM

Hi,

I had an environment Variable ABC set from the command line export ABC=hello

I want to use this in the following way

VER=2000 ABC=$ABC/script/$VER myScript myProgram

After the execution of this line the env wants to remain unchanged. that is
env|grep 'ABC' must show ABC=hello.

Helps will be appreciated !!!

catkin · 12-02-2010, 06:53 AM

Experiment shows no can do; if you assign a value to a variable that is an environment variable then the environment variable is changed. Maybe you are asking us to fix a sub-optimal solution; what do you want to achieve?

Guttorm · 12-02-2010, 07:35 AM

Hi

You can use () so the shell will do a fork. But the variable changing can't be on the same line because the shell will resolve variables before they are changed.

Code:

#!/bin/sh
ABC="hello"
(
VER=2000
ABC=$ABC/script/$VER
echo "ABC=$ABC"
)
echo "ABC=$ABC"

ntubski · 12-02-2010, 11:27 AM

Quote:

Experiment shows no can do; if you assign a value to a variable that is an environment variable then the environment variable is changed

Um

Code:

~$ export ABC=hello
~$ VER=2000 ABC=$ABC/script/$VER sh -c 'echo $VER, $ABC'
2000, hello/script/2000
~$ env | grep ABC
ABC=hello

otheus · 12-02-2010, 11:46 AM

Quote:

Originally Posted by ntubski

Um

Code:

~$ export ABC=hello
~$ VER=2000 ABC=$ABC/script/$VER sh -c 'echo $VER, $ABC'
2000, hello/script/2000
~$ env | grep ABC
ABC=hello

When you told the shell to run a program with a specific environment variable set to whatever, it did exactly that for the new process created. It did not change the environment variable in the current environment.

This is so something like this will work and not screw things up:

Code:

$ export LD_LIBRARY_PATH="/usr/X/lib:/usr/lib"
$ LD_LIBRARY_PATH="/usr/X/compatlib:/usr/compatlib" oldprogram
$ normalprogram

The kernel sees the "compat" version of LD_LIBRARY_PATH when it tries to run "oldprogram", but the default version when it runs "normalprogram".

ntubski · 12-02-2010, 11:54 AM

Quote:

Originally Posted by otheus

When you told the shell to run a program with a specific environment variable set to whatever, it did exactly that for the new process created. It did not change the environment variable in the current environment.

Right, it seemed to me that the OP was in fact asking to not change the environment variable in the current environment even though this is the default behaviour. Possibly I've totally misunderstood what everyone has been saying, if so just ignore me.