On 08/09/2017 09:56 PM, Sam wrote:
> Yes, it's because a space at the end of line:
> 
> --- -^I2017-08-10 10:51:06.097868811 +0800$
>> +++

> but in my match, I add a space, I don't know why it doesn't work.
> 
> AT_CHECK([[awk '/ACTIVE/' stdout | head -4]], [0], [LACP actor_state ACTIVE
>> AGGREGATION SYNC COLLECTING DISTRIBUTING $
>>      partner_state ACTIVE AGGREGATION SYNC COLLECTING DISTRIBUTING $
>> LACP actor_state ACTIVE AGGREGATION SYNC COLLECTING DISTRIBUTING $
>>      partner_state ACTIVE AGGREGATION SYNC COLLECTING DISTRIBUTING $
>> ])$

Because autoconf eats trailing spaces by default (it's a feature).  You
can work around it by TELLING autoconf that you intend for there to be
trailing space:

AT_CHECK(..., [[trailing space preserved here: @&t@
but not here
more text]])

The @&t@ quadrigraph (mnemonic 'and-t' sounds similar to 'empty')
expands to nothing, but is converted after the point when trailing
whitespace is eaten.

The manual documents this:
https://www.gnu.org/software/autoconf/manual/autoconf.html#Quadrigraphs

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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