Rerun execute_process on file change - makefile

Question

I am looking for a way to get CMake to re-run a shell command every time it detects that the dependencies for a specific target/executable has changed. I tried adding a custom command the has a dependency on a target, but this does not seem to be doing the trick.
Example of what I thought might work:
ADD_CUSTOM_COMMAND(
OUTPUT temp
DEPENDS my_Target
COMMAND ./some_command.sh)
Any suggestions of a command that may be able to run a command when a dependency change has been detected for a target. Or even better if we can check for a change in specific files.

Answer 1

From your description, it sounds like you might want this:
cmake_minimum_required(VERSION 2.8)
project(cmaketest)
add_custom_command(OUTPUT some_file.cpp
DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/bar.cpp
COMMAND ${CMAKE_COMMAND} -E copy
${CMAKE_CURRENT_SOURCE_DIR}/bar.cpp
${CMAKE_CURRENT_BINARY_DIR}/some_file.cpp
VERBATIM
)
add_executable(mn main.cpp some_file.cpp)
Put the output file in the source list of the target which depends on it.

Answer 2

add_custom_command() uses simple check for OUTPUT file existence to determine if the command should be run. If it doesn't exist, then CMake do make my_Target and only then run your command. At the same time, if OUTPUT exist, CMake doesn't run anything at all.
To achieve what you want you need to add_custom_target() (probably with ALL keyword to run it with make) and implement checking for changes inside your some_command.sh.