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Re: what is $ac_t ?

From: Eric Blake
Subject: Re: what is $ac_t ?
Date: Fri, 17 Sep 2010 11:01:07 -0600
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On 09/17/2010 10:36 AM, Eric Blake wrote:
On 09/17/2010 10:25 AM, Sam Steingold wrote:
google appears to suggest that $ac_t is widely used in older configure
scripts as a tab character, e.g.:
echo "$ac_t""found" 1>&6
it appears that it it not mentioned in any docs and not defined to
anything useful for some time.

since recently, however, it is used in a loop setting ac_install_sh, and
now it is set to "install-sh". thus now I see configure messages like

checking for getrlimit declaration... (cached) install-shextern int
getrlimit (enum __rlimit_resource, struct rlimit *);

Hmm, on looking at this closer, I only fixed config.status, which happens towards the end of configure, but you are quoting a line that occurs before config.status is created.

What project is this, so I can see the (or, since it may be old enough to not be renamed yet) and the resulting configure file to see what else might be setting ac_t?

By the way, the use of "$ac_t" alongside cache results seems to be weird. The whole idea was that there used to be setups where there was no portable way of printing text without a trailing newline, so for those shells, you'd get:

'checking for ...
', delay, '<tab>result'

for a visual appearance of

checking for ...

which is the best you can do, compared to better shells that do

'checking for... ', delay, 'result'

resulting in the more visually appealing

checking for ... result

But with the placement of $ac_t that you described, that would result in:

'checking for ...
', delay, '(cached) <tab>result'

for an awkward output of:

checking for ...
(cached)        result

rather than the better:

checking for ...
        (cached) result

Finally, I seriously wonder if anyone can even run modern configure scripts on a shell that is so old that it supports neither some echo variant that suppresses newlines, nor printf(1), nor the print builtin. That is, the days where $ECHO_T expands to nothing or tab based on whether $ECHO_C expands to \c or nothing may be over, and we could produce leaner configure scripts by dropping the ECHO_[CT] usage altogether.

Eric Blake   address@hidden    +1-801-349-2682
Libvirt virtualization library

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