.
Last update: 1997-05-20
9945-2-110
_____________________________________________________________________________
Topic: shell - ENV
Relevant Sections: 3.5.3
Defect Report:
-----------------------
From: [email protected]
Date: Wed, 19 Apr 95 17:29:02 EDT
Dear Interpretations Board:
I would like an interpretation of the scope of the ENV
environment variable as described in the 9945-2:1993 Shell
and Utilities Standard.
In Section 3.5.3, page 123, lines 242-252 the standard says,
"This variable, when the shell is invoked, shall be ... This
standard specifies the effects of this variable only for
systems supporting the User Portability Utilities Option."
It isn't clear whether or not, non-interactive shells, and
shell scripts are required to expand and use the ENV file.
Behavior varies from one implementation to another and
overall system performance can be effected.
At the time that the UPE was removed and put into a
separately balloted standard, there was discussion that
indicated that the shell used for system() didn't have to
support UPE extensions even on UPE systems, since portable
scripts could not rely on the UPE. However, if systems that
support UPE require ENV to be expanded for each call to
system(), then this dichotomy into two shells would not be
possible unless the standard is changed to provide an
explicit exception for this.
More importantly, if systems that support UPE are required
to process ENV files for non-interactive shells, then it is
impossible to write scripts that have predictable behavior.
For example, if the ENV file does a set or shift, then the
arguments seen by the script will differ than the ones given
by the user. Unlike, aliases, functions, and options that
are set in the ENV, there is no way for the script to work
around these changes.
In addition, the standard doesn't specify when a shell will
be invoked. For example, if foo is a script, will running
foo invoke a shell? Current implementations vary. Some
implementations will always invoked a new shell. Others,
only if the line, #! /bin/sh is the first line of the
script; others, never. This leads to unpredictable
behavior.
I believe that the standard is unclear about when ENV is to
be used on systems that support the UPE. The current
wording is the result of editorial choice that occurred when
merging two separately balloted standards. The wording in
the standard should be changed to make it clear that for
systems that support UPE, ENV is only required to be used
for interactive shells.
Sincerely yours,
David Korn
David Korn
research!dgk
[email protected]
Interpretation response
------------------------
The standard states the behavior for the ENV environment variable, and
conforming implementations must conform to this. However, concerns have
been raised about this which are being referred to the sponsor.
Rationale:
None
Forwarded to Interpretations group: Apr 20 1995
Proposed resolution circulated: May 16th
Comments due: June 15th
Finalised: June 16th 1995