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Re: exiting noninteractive shells on 'shift 2'

From: Chet Ramey
Subject: Re: exiting noninteractive shells on 'shift 2'
Date: Thu, 8 Nov 2018 19:03:06 -0500
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On 11/8/18 3:37 PM, Eric Blake wrote:
> If I'm reading POSIX correctly, shift is a special built-in utility, and if
> '$#' is 0 or 1, then 'shift 2' counts as a utility error that shall exit
> the shell, per the table in 2.8.1 Consequences of Shell Errors:
> http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_08_01
> dash gets this right:
> $ dash -c 'set 1
>> shift 2
>> echo "oops"'
> dash: 2: shift: can't shift that many
> but bash happily lets 'shift 2' fail with $? set to 1 but continues on with
> execution of the rest of the script, even when in POSIX mode:

As you later note:

"If the n operand is invalid or is greater than "$#", this may be
considered a syntax error and a non-interactive shell may exit; if the
shell does not exit in this case, a non-zero exit status shall be returned.
Otherwise, zero shall be returned."

So the bash behavior is not a conformance issue, and allowed by the

``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    address@hidden    http://tiswww.cwru.edu/~chet/

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