When invoking Make, you can specify which target s you want to build as the goal s by specifying it as a positional argument:. Make provides the. PHONY target syntax to mark a target as not pointing to a file:. If you have multiple phony targets, a good pattern might be to append each to. PHONY prerequisite! Use with caution!! Implicit rules are provided by Make.
You will occasionally encounter them in the wild, so be aware. Pattern rules let you write a generic rule that applies to multiple targets via pattern-matching:. If you use those. As seen above, these are targets that Make will check before running a rule.
They can be files or other targets. In C projects, you might have a rule that converts a C file to an object file, and you want the object file to rebuild if the C file changes:. A very important consideration for C language projects is to trigger recompilation if an include header files change for a C file. See more details here:. If any line of the recipe returns a non-zero exit code, Make will terminate and print an error message.
You can tell Make to ignore non-zero exit codes by prefixing with the - character:. Prefixing a recipe line with will disable echoing that line before executing:. These features are less frequently encountered, but provide some powerful functionality that can enable sophisticated behavior in your build.
There are several functions provided by Make. You can import other Makefile contents using the include directive:. This is often used when building external libraries. Note that approaches using this feature of Make can be quite confusing, adding helpful comments explaining what the intent is can be useful for your future self! VPATH is a special Make variable that contains a list of directories Make should search when looking for prerequisites and targets. It can be used to emit object files or other derived files into a.
You may see the touch command used to track rules that seem difficult to otherwise track; for example, when unpacking a toolchain:. I recommend avoiding the use of touch. However there are some cases where it might be unavoidable. For profiling a make invocation e. If your project includes a lot of compiler flags search paths, lots of warning flags, etc. It can also regenerate, use, and then delete intermediate files which need not be saved.
GNU Make also has a few simple features that are very convenient. Most versions of Make will assume they must therefore recompile all the source files that use the header file; but GNU Make gives you a way to avoid the recompilation, in the case where you know your change to the header file does not require it.
We have developed conventions for how to write Makefiles, which all GNU packages ought to follow. It is a good idea to follow these conventions in your program even if you don't intend it to be GNU software, so that users will be able to build your package just like many other packages, and will not need to learn anything special before doing so. It can also be found on the GNU mirrors ; please use a mirror if possible.
Documentation for Make is available online, as is documentation for most GNU software. A brief summary is available by running make --help. Announcements about Make and most other GNU software are made on info-gnu archive. Security reports that should not be made immediately public can be sent directly to the maintainer.
If there is no response to an urgent issue, you can escalate to the general security mailing list for advice. Development of Make, and GNU in general, is a volunteer effort, and you can contribute. For information, please read How to help GNU. If you'd like to get involved, it's a good idea to join the discussion mailing list see above. We defend the rights of all software users. There are also other ways to contact the FSF. Free Software Supporter :. Make is a tool which controls the generation of executables and other non-source files of a program from the program's source files.
Make gets its knowledge of how to build your program from a file called the makefile , which lists each of the non-source files and how to compute it from other files. When you write a program, you should write a makefile for it, so that it is possible to use Make to build and install the program. As a result, if you change a few source files and then run Make, it does not need to recompile all of your program.
It updates only those non-source files that depend directly or indirectly on the source files that you changed. A rule in the makefile tells Make how to execute a series of commands in order to build a target file from source files.
It also specifies a list of dependencies of the target file. This list should include all files whether source files or other targets which are used as inputs to the commands in the rule. When you run Make, you can specify particular targets to update; otherwise, Make updates the first target listed in the makefile.
Of course, any other target files needed as input for generating these targets must be updated first.
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