> On Monday 23 May 2005 02:04, Deron Meranda wrote: > > > > Environment variables are private to each process. Although each > > process *usually* gets its initial set of variables by copying those > > from it's parent, from that point on they are different. A variable > > lookup does not go "up the chain" of processes...it only looks in the > > current process. > > > > You can see the current set of environment variables in a shell by > > using the "env" builtin command. For non-shell programs there is > > usually a language-dependent method to get to them. In C/C++ for > > instance there is the environ[] array as well as the getenv(3) library > > call. In Python you have the sys.environ dictionary. And so on for > > other languages. > > > > If you want to see the environment variables in some other process > > your choices are more restricted. Given that you have proper security > > permissions, you can look at the /proc/nnnn/environ file, where nnnn > > is the process ID number. The variables are separated by 0-valued > > bytes, so the easiest way to just peek at them is perhaps, > > > > cat /proc/12345/environ | xargs -0 -n 1 echo # that's a > > digit-zero in the "-0" > > > > They are usually listed unsorted, so you can also pipe it through the > > sort command. > > [The above technique is Linux-specific; other Unix-based OS's have > > slightly different mechanisms]. > > > > Now, as far as the export command...the shell (bash and others) is > > really just a simple interactive programming language. Like most > > programming languages it has it's own concept of a "variable". The > > shell's variables are actually distinct from environment variables, > > which the kernel itself keeps. The export command tells the shell > > that you want it to essentially equate the two....meaning that > > whenever you change the value of a shell variable, it will also > > implicitly change the value of a equivalently named environment > > variable. Environment variables will be inherited by any child > > processes the shell happens to start, shell variables will not be. > > > > Incidentally you only need to export a variable once; you don't need > > to keep exporting it every time you change it's value. > > -- > > Deron Meranda > > This is by far the most complete and understandable explanation > of environment > variables and exporting. Not just answers the question, but also lets one > learn the concept behind it. I just wish that there be as many as > possible > such good answers on the list... :-)) Yes. It is very detailed. Here are a couple of minor details to add to what's above. If a user exports an environment variable from a terminal it's only good for that terminal. linux@example% export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:lib The above line sets the environment variable LD_LIBRARY_PATH to the current LD_LIBRARY_PATH plus the relative lib directory. If you're using the bash shell, to view an entire list of environment variables for a terminal just type "export". To make permanent changes to environment variables, again if using the bash shell, the user can go to their home location and edit the .bashrc file. .bashrc example: LD_LIBRARY_PATH=$LD_LIBRARY_PATH:home/linux/lib After adding the above line to the .bashrc file, the load library path will be the same for every terminal and doesn't have to be set each time a new terminal is opened. If you want this path to be available to any terminal that is open you will have to "source .bashrc" at the command prompt. Otherwise, just close all active terminals and open new ones.
