[vox-tech] ksh question

[Jeff Newmiller]

On Fri, 25 Jan 2002, Jay Strauss wrote:

> Ok, a question guaranteed not to get flamed, or start a war.
> 
> I want one environmental variable to equal another (dynamically all the
> time) but I can't figure it out.  That is I want the behavior of:
> 
> export PS1='$PWD'

This behavior is well-defined... PS1 expands to a dollar sign followed by
PWD.  What is also well-defined, but may not behave in the fashion you
seem to want, is the subsequent expansion by BASH of the contents of this
variable before display.  That is, you always have to evaluate the
contents of the variable, as well as evaluating the variable.

> For example, this is what I'd like to happen (though I can't get it to
> work):
> 
> pete=one
> repeat=$pete
> echo $repeat
> one
> pete=two
> echo $repeat
> two

In bash, you can do:

  $ var=value
  $ ref=var
  $ echo ${!ref}
  value

but unfortunately, you cannot do

  $ ${!ref}=anothervalue

(see http://www.linuxdoc.org/LDP/abs/html/bash2.html#EX78)

I don't know ksh, but playing around with it I find:

  $ echo `eval 'echo $'$ref`
  value

seems to work.

Thus, the script receiving the indirect reference variable must be
constructed to handle the indirection.

You probably wouldn't want to be doing this with an suid script... you
could find yourself evaluating unfriendly shell code. :(

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