Re: Recommended way to truncate a shell variable value in autoconf

[Eric Blake]

On 02/21/2014 03:26 PM, Eric Blake wrote:
> On 02/21/2014 03:23 PM, Eric Blake wrote:
>> On 02/21/2014 03:08 PM, Dale Visser wrote:
>>> I have a macro argument that I would like to place in a shell variable, but 
>>> with a catch. I want to truncate it at the first space or comma. I have 
>>> code that works for me (in Ubuntu), like this:
>>>
>>>     my_var="$1"
>>>     my_var=${my_var%%\ *}
>>>     my_var=${my_var%%,*}
>>>
> 
>> If you guarantee that your shell is capable (right now, that could be
>> done by using the undocumented _AS_DETECT_REQUIRED macro), then your way
>> is portable.  Until then, the only portable fallback to this particular
>> problem is the use of 'expr' pattern matching and/or sed scripts.  :(
> 
> Or mess with IFS splitting:
> 
> my_var=$1
> IFS=' ,'
> set dummy $my_var
> shift
> IFS=' ''      ''
> '
> my_var=$1

Oh, and be sure to use 'set -f' for the duration of your IFS splitting,
to avoid globbing.

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

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