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Re: bash 'let' can give error


From: Eric Blake
Subject: Re: bash 'let' can give error
Date: Fri, 10 Dec 2010 08:14:35 -0700
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On 12/09/2010 10:52 AM, Dominic Raferd wrote:
> Description:
> 
> $ val=0; let val++; echo $val,$?; unset val
> 1,1

Not a bug.

> 
> see the error code 1. Setting any other start value (except undefined)
> for val does not produce this error, the problem occurs for let val++
> and let val-- if the start value is 0.

let intentionally returns status 1 if the value was 0; and status > 1 if
there was an error.  Why?  So you can do loops such as:

countdown=10
while let countdown--; do ... ; done

> Why does this happen? Is it 'by design'?

Yes.  The same as for 'expr' which is standardized by POSIX to have the
same behavior.

-- 
Eric Blake   address@hidden    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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