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Re: Problem with brace expansion

From: Eric Blake
Subject: Re: Problem with brace expansion
Date: Tue, 21 Apr 2015 17:22:12 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0

On 04/21/2015 01:44 PM, Dr Alun J. Carr wrote:

> Tests were done with bash, ksh, zsh, pdksh, dash and heirloom System V Bourne 
> sh with the following versions:
> bash  3.2.57(1)
> bash  4.3.33(1)
> ksh           version         sh (AT&T Research) 93u+ 2012-08-01
> zsh           5.0.5 (x86_64-apple-darwin14.0)
> pdksh stable 5.2.14
> dash  stable 0.5.8
> sh            ???

You do realize, I hope, that brace expansion is not required by POSIX,
and therefore there is no standard for what behavior it has, and it
should be no surprise that pdksh, dash, and Bourne sh do not try to
expand it.

As for whether bash should expand $n into 4 prior to doing brace
expansion, or whether brace expansion is attempted first but not
recognizing $n as a valid bound devolves into no expansion, that is
indeed a difference between ksh and bash.  But bash is consistent with
its documentation:

>        The order of expansions is: brace expansion; tilde expansion, parameter
>        and variable expansion, arithmetic expansion, and command  substitution
>        (done  in a left-to-right fashion); word splitting; and pathname expan‐
>        sion.

so you cannot use a variable as a bound and still expect brace expansion
to work, since variables aren't expanded yet.

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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