[Discuss] rsync v. cp in data migration

[gaf at blu.org (Jerry Feldman)]

On 05/25/2013 11:42 AM, Derek Martin wrote:
> One last point:
>
> On Sat, May 25, 2013 at 09:32:02AM -0400, Greg Rundlett (freephile) wrote:
>> # we will use a prepared file 'users' whose contents are a list of users,
>> one user per line
>> while read USER
> The variable $USER is set for you by the system when you log in, and
> some things may depend on it (this is a very old Unix feature, and
> I've forgotten which--most things should no longer do this, for the
> reason I'm describing now).  If you change the value of $USER, any
> such things may break.  Generally the convention is to use upper case
> names for environment variables (i.e. things you want to have
> persistence across sessions/processes/etc.), and shell scripts should
> use lower case names for their variables to avoid unintended conflicts
> like this.
Yes, using upper case for environment variables and lower case for local 
variables is the long-time Unix/Linux convention. Shell scripts can use 
both local as well as environment variables. I think your definition of 
persistence is incorrect.
Environment variables persist within the process where they were 
created, and any child process. However, a child process cannot affect 
an environment variable in a parent or sibling process. There are a few 
builtin environment variables. HOME and USER are two that are used 
frequently.

-- 
Jerry Feldman <gaf at blu.org>
Boston Linux and Unix
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