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Re: Content-based dependencies

From: Mike Shal
Subject: Re: Content-based dependencies
Date: Wed, 6 May 2009 01:00:18 -0400

On 5/6/09, Yang Zhang <address@hidden> wrote:
> Is there a way to have GNU make cache copies of source files, so that when
> rules are triggered by timestamp comparisons between targets and sources, it
> will also compare the current source with the cached source to make sure
> that it actually changed before executing the actions (only executing if
> they differ)?

This sounded familiar - I found some older threads on the issue:

Also the solution here may work for you:

Ultimately what is your goal here? Are you trying to avoid the "change
a comment in a header rebuilds everything" issue, or do you have some
other timestamp problems? Keep in mind that doing a diff or using a
checksum to determine out-of-dateness isn't exactly cheap - you may be
trying to optimize a corner case to the detriment of the general case.


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