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c shell script; Howto use environement variables to build environment variables and take their value

c shell script; Howto use environement variables to build environment variables and take their value

Post by Gert villem » Fri, 01 Feb 2002 22:17:09



In a script I wish to specify two environment variables like this;

setenv FOO bee
setenv ${FOO}_ROOT /home/bee

This is ok and will set "FOO=bee" and "bee_ROOT=/home/bee".

Now I wan't to build the "bee_ROOT" variable using "FOO" and use the
value in a expression, i.e. something like this;

source ${${FOO}_ROOT}/.cshrc

This will not execute. The error is "Variable syntax". It seems that
the shell cannot figure to evaluate the inner ecpression first and
then the outer. I have tried different combination of forcing
evaluation with '' and assigning to variable first etc, but with
little luck.

Any idea/explanation why this is not possible/what I can do instead?

Cheers,
Gert.

 
 
 
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c shell script; Howto use environement variables to build environment variables and take their value

Post by Seb » Fri, 01 Feb 2002 22:22:42


eval source \${${FOO}_ROOT}/.cshrc

--Seb



Quote:> In a script I wish to specify two environment variables like this;

> setenv FOO bee
> setenv ${FOO}_ROOT /home/bee

> This is ok and will set "FOO=bee" and "bee_ROOT=/home/bee".

> Now I wan't to build the "bee_ROOT" variable using "FOO" and use the
> value in a expression, i.e. something like this;

> source ${${FOO}_ROOT}/.cshrc

> This will not execute. The error is "Variable syntax". It seems that
> the shell cannot figure to evaluate the inner ecpression first and
> then the outer. I have tried different combination of forcing
> evaluation with '' and assigning to variable first etc, but with
> little luck.

> Any idea/explanation why this is not possible/what I can do instead?

> Cheers,
> Gert.


 
 
 
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c shell script; Howto use environement variables to build environment variables and take their value

Post by Tinti » Sat, 02 Feb 2002 06:26:50



Quote:> In a script I wish to specify two environment variables like this;

> setenv FOO bee
> setenv ${FOO}_ROOT /home/bee

> This is ok and will set "FOO=bee" and "bee_ROOT=/home/bee".

> Now I wan't to build the "bee_ROOT" variable using "FOO" and use the
> value in a expression, i.e. something like this;

> source ${${FOO}_ROOT}/.cshrc

> This will not execute. The error is "Variable syntax". It seems that
> the shell cannot figure to evaluate the inner ecpression first and
> then the outer. I have tried different combination of forcing
> evaluation with '' and assigning to variable first etc, but with
> little luck.

> Any idea/explanation why this is not possible/what I can do instead?

http://www.grymoire.com/Unix/CshTop10.txt
 
 
 
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1. How to get value of environment variable in variable name?

I have the name of an environment variable in a shell script variable,
and would like to get at the value of that environment variable.  This
happens to be in a ksh script, but I'm looking for a generic solution
that would also work in the standard Bourne shell (i.e, not a ksh
specific solution).  In Perl, this is trivial, but I haven't found the
right incantation of eval or backticks or indirection to get this
working.

For example, if I have an environment variable named BAR whose value is
"foo", and I have a script variable named var whose value is "BAR", how
do I assign "foo" to another variable in the script?

  var=BAR
  value=???

Thanks,
Alfred

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