[newbie] setenv / env ?

[Jose Ricardo Sabino]

        I installed the Mesa Opengl package and in the README file is proposed the 
lib path  $TOP/lib become the enviroment variable LD_LIBRARY_PATH. Well, when 
I try the following:

# setenv LD_LIBRARY_PATH $TOP/lib

I got:

bash: setenv: command not found 

otherwise, I run the following:

# env LD_LIBRARY_PATH $TOP/lib
I got:

env: LD_LIBRARY_PATH: No such file or directory

My question is:

 How to set the enviroment var. LD_LIBRARY_PATH?

thanks very much any help!

ze