export which is correct syntax

[Suvayu Ali]

On Sat, Jan 04, 2014 at 03:51:02PM +0000, Dave Mitchell wrote:
> On Sat, Jan 04, 2014 at 04:08:17PM +0100, Suvayu Ali wrote:
> > On Sat, Jan 04, 2014 at 10:37:48PM +1030, Tim wrote:
> > > Frank Murphy:
> > > > > 1: export TMPDIR=/var/tmp
> > > > > 2: export TMPDIR=$TMPDIR:/var/tmp
> > > 
> > > Suvayu Ali:
> > > > Depends on what you want to do.  If you want to overwrite the variable,
> > > > use (1).  If you want to add (prepend) to the variable, use (2).
> > > 
> > > Wouldn't that actually be an append - add onto the end of the existing
> > > variables, as opposed to insert before the existing variables (prepend).
> > 
> > This would be append:
> > 
> > 3: export TMPDIR=/var/tmp:$TMPDIR
> > 
> > This is how I understand it; if a matching path is found, it is
> > considered for the task at hand.  So prepend (front) would mean "I want
> > this to be considered before everything else", whereas append (back)
> > would mean "I want this to be considered when everything else fails".
> > 
> > The easiest example to see it in action is the PATH variable.
> > 
> > Does that make sense?
> 
> No.
> 
>     TMPDIR=/tmp
>     ..
>     export TMPDIR=/var/tmp:$TMPDIR
> 
> TMPDIR now contains /var/tmp:/tmp and the new path (/var/tmp) is earlier
> in the search than the existing value(s) and will be used in preference to
> /tmp. So /var/tmp has been *pre*pended to the search path by any
> definition I can think of.

Oops!  Not sure where my mind is today; you are right.  I was thinking
the *new* value is in TMPDIR for some inexplicable reason!

-- 
Suvayu

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