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POHow do I tell SCons to ignore implicit dependencies from command actions?
 

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  1. POHow do I tell SCons to ignore implicit dependencies from command actions?
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    <p>By default, SCons seems to look at the 'recipe' used to build a program and extracts implicit dependencies from it. For example suppose my SConstruct contains:</p> <pre><code>Command('foo', 'foocreator.py', '/usr/bin/python foocreator.py &gt; foo') </code></pre> <p>And I've already built 'foo' ('foo' is up to date). Now I change SConstruct (or more realistically, pass different options) so that the command for 'foo' becomes:</p> <pre><code>Command('foo', 'foocreator.py', '/usr/bin/qrsh -V -cwd /usr/bin/python foocreator.py &gt; foo') </code></pre> <p>(In other words, run the foocreator.py script through SGE) Now SCons tries to rebuild foo, --debug=explain tells me that this is because of a "new dependency on /usr/bin/qrsh" and a "dropped dependency on /usr/bin/python").</p> <p>How can I prevent this inference of dependencies from the recipe, preferably globally? So far I haven't even been able to find a specification of this behaviour. I don't want to have to spell out the fact that 'foo' doesn't really depend on python or qrsh, because I would have to do that for every target and for every possible location of those programs. There must be a "right" way.</p> <p><strong>EDIT</strong>: I have also now tried explicitly adding Ignores for each target, as in:</p> <pre><code>Ignore('foo', '/usr/bin/python') Ignore('foo', '/usr/bin/qrsh') </code></pre> <p>and even this doesn't work! SCons still wants to rebuild everything whenever I switch between running through qrsh and not.</p>
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    1. CODoes SCons try to rebuild foo always, or just after changing the Command() action? If its only after changing the action, then that sounds quite reasonable to me.
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    2. CO@Brady only when the action "changes". It would do the same thing even if the environment changed such that a different version of python (or gcc, or whatever) were being used. I agree that the behaviour is useful in many cases, I just want to know how to turn it off.
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