l i n u x - u s e r s - g r o u p - o f - d a v i s
Next Meeting:
July 7: Social gathering
Next Installfest:
Latest News:
Jun. 14: June LUGOD meeting cancelled
Page last updated:
2002 Jan 26 20:50

The following is an archive of a post made to our 'vox-tech mailing list' by one of its subscribers.

Report this post as spam:

(Enter your email address)
Re: [vox-tech] ksh question
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [vox-tech] ksh question

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}

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`

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. :(

Jeff Newmiller                        The     .....       .....  Go Live...
DCN:<jdnewmil@dcn.davis.ca.us>        Basics: ##.#.       ##.#.  Live Go...
                                      Live:   OO#.. Dead: OO#..  Playing
Research Engineer (Solar/Batteries            O.O#.       #.O#.  with
/Software/Embedded Controllers)               .OO#.       .OO#.  rocks...2k

vox-tech mailing list

LUGOD Group on LinkedIn
Sign up for LUGOD event announcements
Your email address:
LUGOD Group on Facebook
'Like' LUGOD on Facebook:

Hosting provided by:
Sunset Systems
Sunset Systems offers preconfigured Linux systems, remote system administration and custom software development.

LUGOD: Linux Users' Group of Davis
PO Box 2082, Davis, CA 95617
Contact Us

LUGOD is a 501(c)7 non-profit organization
based in Davis, California
and serving the Sacramento area.
"Linux" is a trademark of Linus Torvalds.

Sponsored in part by:
O'Reilly and Associates
For numerous book donations.