Making CMake print commands before executing

Question

I'm working on a large C++ project built with CMake on Linux. CMake runs okay, producing a horde of Makefiles in the tree of modules and applications. Running GNU make leads to linker errors. How can I get make to print out the exact commands before running them?

The -d option does not print the commands, but plenty of information that hasn't been helpful.

The -n option prints all the commands, but does not run them, so I can't tell were exactly the trouble is. Examining the stdout from make -n, I don't see any commands that are relevant. I suspect some commands change depending on the results of earlier commands, and the hierarchy of Makefiles makes it difficult to tell what's really going on.

I don't see any other options in make's man page that seem helpful.

Answer 1

For automake-generated Makefiles, try:

make V=1

Answer 2

An option, which applies to GNU make and works with any Makefile, whether generated by CMake or not, is to use the --trace option to make. This will print out the commands make is executing and still execute them.

This applies to all commands, not just those that VERBOSE=1 or V=1 triggers the printing of in CMake/automake generated makefiles.

And yet another alternative on Linux is to run make under strace, as strace -f -e trace=execve make <make options>. The output from strace will include every process that is executed, by make, by a shell script that make ran, etc.

For instance, you might find that the CMake-generated makefile executes /usr/bin/cmake -E __run_co_compile <lots of options ...> and still wonder what the exact compiler invocation(s) are that this in turn will run. You can get that with the strace method.

Answer 3

Fairly sure this will work:

make VERBOSE=1

You should also be able to add this to your CMakeLists.txt to permanently set that.

set(CMAKE_VERBOSE_MAKEFILE on)

This is covered in the CMake FAQ.