Hey, I'm trying to figure this one out. Maybe you can help me. Here's what I got:
-----------------------------
#!/bin/bash
echo "Enter the partition where LFS is to be installed (/mnt/lfs):"
read LFS
if [ ! $LFS ]
then
LFS="/mnt/lfs"
fi
export LFS
-----------------------------

Now, when I run this, it works fine, however, when it exits back to the shell, I type in "echo $LFS" and it prints an empty line. It's my undestanding that LFS should be a global variable and should be available after the program exits. Am I wrong?

Are shell scripts not run in a new instance of the shell? Why not just follow the LFS book's way of doing it via sourcing files?

Actually, I haven't yet started the installation of LFS, this is just a generic question regarding global variables. But, yes, my plans are to create an automatic install script. Why? Because I've gone through the whole thing 4 times now, and it's getting boring.

There is already a full project towards automating the build, you can find links through the LFS homepage. There is also a Makefile available at Christophe Devine's (?) home directory on the main LFS server.

To answer your question more fully: the script is launched in a new instance of the shell, and thus is not affecting your current instance. However, any script run from within that sub-shell will have that environmental variable ( as far as I know ).

You seem to be misunderstanding how environment variable works. They are not global to the system. Rather, each process inherits a copy of the parent's envvars. So in your case, when the child script exits, any envvars it creates are also lost.

Thank-you for your explanations. They were very helpful. In regards to ALFS, I've tried many times to install it, but I run Mandrake 9.2 and there's a universal law that says ALFS does not install under Mandrake 9.2. We always get an error with libxml2. Anyway, my script is teaching me a lot about bash programming, which is always a plus.

exports only work in the script as it runs.
everything until the script ends will 'see' the export.
When the script dies so do it's exports.


But FYI

to make the export work you can 'dot' the file.

. script.sh

this, sort of 'in lines' a script without running explicitly.

it will work, but be careful you don't put exit or return commands in
or it will log you out!

but one generally uses dot files just for environment and aliases and such.
simple stuff.

you can also make it as a function:

o_func_it()
{
read input
export LFS="$input" # quotes are safer!
}

put that in a file and 'dot' it and then you can type
"o_func_it"
like you would a command.

functions are a good idea in scripting, but generally one doesn't
do them as above, just from the login shell. but they are interesting to
try out.

have a really *good* read of 'man bash' and try it all.


regards, billy


billy