Add files in sub folders to target - cmake

Question

I'd like to add output files in subdirectory to a build target.
I wrote in CMakeLists.txt like below:
file(GLOB srcfiles "src/*.txt")
add_custom_target(subtask ALL)
set(dest_dir ${PROJECT_SOURCE_DIR}/sub/)
foreach(srcfile ${srcfiles})
string(REGEX REPLACE "^.*/(.*).txt$" filename ${srcfile})
add_custom_command(OUTPUT ${dest_dir}/${filename}.txt
COMMAND ${CMAKE_COMMAND} ARGS -E make_directory ${dest_dir}
COMMAND ${PROJECT_SOURCE_DIR}/process.sh ARGS ${srcfile}
MAIN_DEPENDENCY ${PROJECT_SOURCE_DIR}/process.sh)
add_dependencies(subtask ${dest_dir}/${filename}.txt)
endforeach(srcfile)
And executed:
mkdir build && cmake .. && make
But sub/*.txt are not created after build.
How should I do to build all commands on build?
updated (2017/2/4)
I solved the issue: use add_custom_command for each target and then declare add_custom_target that depends on all targets of add_custom_command.
set(TARGET_FILES "")
file(GLOB SRC_FILES "src/*.txt")
foreach(SRC_FILE ${SRC_FILES})
string(REGEX REPLACE "^.*/(.*).txt$" "\\1-foo.txt" TARGET_FILE ${SRC_FILE})
add_custom_command(
OUTPUT ${PROJECT_SOURCE_DIR}/sub/${TARGET_FILE}
COMMAND ${CMAKE_COMMAND} ARGS -E make_directory ${PROJECT_SOURCE_DIR}/sub
COMMAND ${PROJECT_SOURCE_DIR}/process.sh ARGS ${SRC_FILE}
MAIN_DEPENDENCY ${PROJECT_SOURCE_DIR}/process.sh)
list(APPEND TARGET_FILES "${PROJECT_SOURCE_DIR}/sub/${TARGET_FILE}")
endforeach()
add_custom_target(foo_txt ALL DEPENDS ${TARGET_FILES})

Answer 1

It's a little unclear what you are trying to achieve, but just from looking at it I would say it should be:
set(dest_dir ${PROJECT_SOURCE_DIR}/sub)
add_custom_target(
subtask ALL
COMMAND ${CMAKE_COMMAND} -E make_directory ${dest_dir}
COMMAND ${PROJECT_SOURCE_DIR}/process.sh
)
Only if the output.txt is an input for something else, you need a custom command:
set(dest_dir ${PROJECT_SOURCE_DIR}/sub)
add_custom_command(
OUTPUT ${dest_dir}/output.txt
COMMAND ${CMAKE_COMMAND} -E make_directory ${dest_dir}
COMMAND ${PROJECT_SOURCE_DIR}/process.sh
MAIN_DEPENDENCY ${PROJECT_SOURCE_DIR}/process.sh
)
add_custom_target(
subtask ALL
DEPENDS ${dest_dir}/output.txt
)
Note that the default working directory for those commands is CMAKE_CURRENT_BINARY_DIR.
Edit: I think the problem in your code is the use of add_dependencies() for file level dependencies. But add_dependencies() can only be used to declare target dependencies.
Edit: With a foreach() you can either collect the dependencies or APPEND them with to a dummy output. The first looks something like this:
file(GLOB srcfiles "src/*.txt")
set(dest_dir "${PROJECT_SOURCE_DIR}/sub")
file(MAKE_DIRECTORY "${dest_dir}")
foreach(srcfile ${srcfiles})
get_filename_component(filename "${srcfile}" NAME_WE)
add_custom_command(
OUTPUT "${dest_dir}/${filename}.txt"
COMMAND ${PROJECT_SOURCE_DIR}/process.sh ${srcfile}
MAIN_DEPENDENCY "${srcfile}"
DEPENDS "${PROJECT_SOURCE_DIR}/process.sh"
WORKING_DIRECTORY "${dest_dir}"
)
list(APPEND subtask_deps "${dest_dir}/${filename}.txt")
endforeach(srcfile)
add_custom_target(
subtask ALL
DEPENDS ${subtask_deps}
)