Why does CMake prefixes spaces with backslashes when executing a command?

Question

I have a custom command in a CMakeLists.txt :

set(testfiles "test1 test2")
add_custom_target(testtouch COMMAND touch ${testfiles})

When I run "make testtouch VERBOSE=1" I see that it executes :

touch test1\ test2

This is just an example, but I have this problem in a real project and the "\ " are breaking the command. Note that I get the variable (here testfiles) from a Find script and can't just get rid of the double quotes.

Why does CMake do that ?

How to avoid it ?

Answer 1

Because sometimes difference between cmake list variable type and cmake string literal become important.

Try to change the variable setup to the following to avoid the problem:

set(testfiles "test1" "test2")

Answer 2

I was trying something similar with multiple arguments some are strings and some are not, i.e.:

add_custom_target(externalProject COMMAND make -s VALUE1:="${argument1}" VALUE2:=${argument2} VALUE3:="${argument3}" ...)

Where argument3 contained "VAL1 VAL2 VAL3".

I found that replacing the spaces with semicolons ; resolved the issue for me when cmake creates the makefile.