How to get a clean environment in a ksh shell?

Question

I need to get rid of all the environment variables in a Ksh shell. I can fork a new instance, but it will inevitably source some init files (as far as I know .profile, .kshrc). Is there a way to bypass the sourcing of those files and any other file that might be read at init time?

Ksh version: Version M-11/16/88i
OS: Solaris 10

Hope I'm clear enough.

Gilles 'SO- stop being evil' · Accepted Answer · 2011-11-02T22:06:14.017

7

~/.profile is only read by login shells. ~/.kshrc is only executed for interactive shells.

Solaris's env supports the syntax (now deprecated, but retained in Solaris, which takes backward compatibility seriously) env - /path/to/command to run /path/to/command in an empty environment. So env - /usr/bin/ksh -c /path/to/script will run the script in an empty environment and will not source any profile script. Ksh might set some environment variables on its own initiative: I don't know about ksh88, but ksh93 sets _ and PWD, and pdksh sets _ and PATH.

You can selectively or indiscriminately clear environment variables from inside ksh.

unset x
for x in $(typeset +x); do
  unset $x
done

edited Nov 02 '11 at 22:06

answered Nov 02 '11 at 21:42

Gilles 'SO- stop being evil'

829,060

env - /path/to/command is a standard compliant syntax, unless I misunderstand what you means. – jlliagre Nov 02 '11 at 21:59
@jlliagre It is? Oh, it was but now it's been withdrawn in favor of env -i. – Gilles 'SO- stop being evil' Nov 02 '11 at 22:05
@Gilles: As usual your explanations are perfect. Is there a way to publicly thank you for everything you've (directly and indirectly) taught me in the course of the past three months? :) – rahmu Nov 02 '11 at 22:34
@rahmu Use your newfound knowledge or your knowledge of other topics to provide good answers to other people's questions. Or otherwise make the Internet a better place. Or otherwise make the world a better place. – Gilles 'SO- stop being evil' Nov 03 '11 at 00:30

sr_ · Answer 2 · 2011-11-03T12:13:24.917

5

me@local:~ $ env - /path/to/shell
$ env
_=/usr/bin/env
PATH=/usr/bin:/bin
RANDOM=24395
$

Notes:

I used a shell to have a look at the resulting environment, any command can be used (guess what env - /usr/bin/env returns)
(@jlliagre's comment:) env is a POSIX standard command.

Edit Clarified the answer.

edited Nov 03 '11 at 12:13

answered Nov 02 '11 at 14:51

sr_

15,384

Unfortunately I couldn't find it on Solaris. – rahmu Nov 02 '11 at 16:11
@rahmu According to the man pages (I don't have Solaris 10 to check), all versions of Solaris since at least 2.4 support env -. Run /usr/bin/ksh and not mksh, of course. – Gilles 'SO- stop being evil' Nov 02 '11 at 21:43
Indeed, env is a POSIX standard command so definitively in Solaris (including 10 and newer). – jlliagre Nov 02 '11 at 21:57
Oh I got mislead by the mksh. I thought it was an executable that "cleaned" the environment :-/ In this case, the answer seems correct. – rahmu Nov 02 '11 at 22:29

How to get a clean environment in a ksh shell?

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