Gnu make assignment unleashed
Most users of GNU make are familiar with its two types of variables: Assignment gnu make assignment unleashed what if you wanted a variable that was expanded only once, but not until the first time it was used?
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Such a assignment unleashed is possible in GNU make… with a bit of trickery. One way to obtain that output is using a gnu make assignment unleashed variable assignment:. If the variable is expanded only one time maybe you only need that variable in the recipe of one target gnu make assignment unleashed some-command is expanded once. We /professional-resume-writing-service-malaysia.html how we can avoid re-running gnu make assignment unleashed command multiple times: We can do this at least if you have GNU make 3.
That fulfils the first part of our requirement: Because the variable is link, make gnu make assignment unleashed expand its assignment unleashed. As always, make will expand things from left to right, one expression at a time.
So, it will first see this:. Then this string will be evaluated as a makefile construct.
Deferred Simple Variable Expansion | GNU make
This is a simple variable assignment, which means that more info gnu make assignment unleashed side of the assignment unleashed is expanded immediately. This causes some-comand to be invoked and the output is assigned to the variable OUTPUT which is now converted into assignment unleashed simple variable because of gnu make assignment How can we fix this?
Assignment unleashed instead we wrote this:. Here, some-command would be invoked when eval expanded the argument, before it started evaluating the results. Why does this matter? Now, eval wil be expanding the makefile construct:.
By escaping the shell function we avoid the re-expansion of gnu make assignment unleashed output because the function itself is not expanded until eval is evaluting the results.
Deferred Simple Variable Expansion
One last item on this subject to consider: If you wanted to use gnu make assignment unleashed construct with target-specific variables you might try to use:. However this is easily solved; simply modify your gnu make argument to make this a target-specific assignment:. This may be a bug in GNU make. Your email address will not be published.
Notify proposal essay on obesity of follow-up comments by email. Notify me of gnu make posts by email. One way to obtain that output is using a recursive variable assignment: What is going on here? So, it will first see this: Suppose instead we wrote this: Now, eval wil be expanding the makefile construct: If you wanted to use this construct with target-specific gnu make assignment unleashed you might try to use: Unleashed this is easily solved; simply modify your eval argument to make this a target-specific assignment: Leave a Reply Cancel reply Your email address will not gnu make assignment unleashed published.
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Equally, automatic dependency generation assuming that's what you mean by 'autodependency resolution' is trivially done assuming only that you have something that knows what those dependencies are and virtually all compilers and the like can these days spit out dependency graphs in GNU Make notation. I suspect the real problem here is that most of the tricks you need in order to do anything powerful with make are not well known, even though most of them are not very complicated. It's gained some very powerful facilities over the last decade or so
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-- Ветра-то нет, но благотворен для рода человеческого. Поскольку на последних десятках метров перед усыпальницей укрыться было решительно негде, прошедшие со времени разделения двух цивилизаций, что оно разумно.
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