(Fwd) [shell] posix conformance for special built-ins

[Bart Schaefer <schaefer@xxxxxxxxxxxxxxxx>]

--- Forwarded mail from David Korn <dgk@xxxxxxxxxxxxxxxx>

Date: Mon, 29 Mar 2004 10:00:27 -0500 (EST)
From: David Korn <dgk@xxxxxxxxxxxxxxxx>
To: shell@xxxxxxxxxxxxxxxx
Subject: [shell] posix conformance for special built-ins 

Subject: posix conformance for special built-ins 
--------

Here is an excerpt from mail from a user that shows different results
for different shells.
> 
> In two places, I have a construct like this:
> 
> 	. foo || source foo || true
> 
> To my surprise, in testing I found that ksh bails out with an error if
> foo does not exist, rather than simply succeeding because of the true
> at the end of the conditional.  Here is what I found for various shells:
> 
> 	$ ksh88
> 	$ . foo || source foo || true
>         /bin/ksh: foo:  not found
>         $ echo $?
>         1
> 
> 	$ ksh93
>         $ . foo || source foo || true
>         /bin/ksh: foo:  not found
>         $ echo $?
>         1
> 
>         $ bash
>         $ . foo || source foo || true
>         bash: foo: No such file or directory
>         bash: foo: No such file or directory
>         $ echo  $?
>         0
> 
>         $ zsh
>         % . foo || source foo || true
>         .: no such file or directory: foo
>         source: no such file or directory: foo
>         % echo  $?
>         0
> 
>         % /bin/sh
>         $ . foo || source foo || true
>         foo: not found
>         $ echo $?
>         1
> 
>         % pdksh
>         $ . foo || source foo || true
>         pdksh: .: foo: not found
>         $ echo $?
>         1
> 
>         $ csh
>         . foo || source foo || true
>         /usr/local/bin/.: Permission denied.
>         foo: No such file or directory
>         echo $status
>         1
> 
>         $ tcsh
>         % . foo || source foo || true
>         /usr/local/bin/.: Permission denied.
>         foo: No such file or directory.
>         % echo $status
>         1
> 
> So, is the behavior of ksh88 and ksh93 in ". foo || source foo || true"
> a bug or a feature?
> 
> -----------------------------------------------------------------------------
> - Nelson H. F. Beebe                    Tel: +1 801 581 5254
> - University of Utah                    FAX: +1 801 581 4148
> - Department of Mathematics, 110 LCB    Internet e-mail: beebe@xxxxxxxxxxxxx
> - 155 S 1400 E RM 233                       beebe@xxxxxxx  beebe@xxxxxxxxxxxx
> - Salt Lake City, UT 84112-0090, USA    URL: http://www.math.utah.edu/~beebe
> -----------------------------------------------------------------------------
> 

This behavior is required by the POSIX and X/Open standards.  In section
section 2.8.1 of the 1003.1-2001 standard  it states,
"For a non-interactive shell, an error condition encountered by a
special built-in shall cause the shell to write a diagnostic message
to standard error and exit as shown in the following table:"
In the following table, it lists Dot script not found, "Shall Exit".

While I don't like this behavior, it was inherited from the Bourne shell.
The standard added 'command' to get around this behavior, so that
	command . foo || source foo || true
would give you the behavior that you want.

So unless we can get the standard changed we are stuck with this behavior.
Thus, bash and zsh are non-conforming.  It would be nice to say that
the shell only bails out in cases for which set -e would have caused
it to exit, but this would require a change to the standard.

David Korn
dgk@xxxxxxxxxxxxxxxx
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---End of forwarded mail from David Korn <dgk@xxxxxxxxxxxxxxxx>

--- Forwarded mail from chet@xxxxxxxxxxx

Date: Mon, 29 Mar 2004 11:37:35 -0500
From: Chet Ramey <chet@xxxxxxxxxxxxxxxxxx>
To: dgk@xxxxxxxxxxxxxxxx
Subject: Re: [shell] posix conformance for special built-ins
Cc: shell@xxxxxxxxxxxxxxxx
Reply-To: chet@xxxxxxxxxxx

> This behavior is required by the POSIX and X/Open standards.  In section
> section 2.8.1 of the 1003.1-2001 standard  it states,
> "For a non-interactive shell, an error condition encountered by a
> special built-in shall cause the shell to write a diagnostic message
> to standard error and exit as shown in the following table:"
> In the following table, it lists Dot script not found, "Shall Exit".
> 
> While I don't like this behavior, it was inherited from the Bourne shell.
> The standard added 'command' to get around this behavior, so that
> 	command . foo || source foo || true
> would give you the behavior that you want.
> 
> So unless we can get the standard changed we are stuck with this behavior.
> Thus, bash and zsh are non-conforming.  It would be nice to say that
> the shell only bails out in cases for which set -e would have caused
> it to exit, but this would require a change to the standard.

This is one of the things bash enables in `posix mode'.

Chet

-- 
``The lyf so short, the craft so long to lerne.'' - Chaucer
( ``Discere est Dolere'' -- chet )
						Live...Laugh...Love
Chet Ramey, ITS, CWRU    chet@xxxxxxxxxxx    http://tiswww.tis.cwru.edu/~chet/
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---End of forwarded mail from chet@xxxxxxxxxxx