CMake add_custom_command not being run

Question

I'm trying to use add_custom_command to generate a file during the build. The command never seemed to be run, so I made this test file.

cmake_minimum_required( VERSION 2.6 )

add_custom_command(
  OUTPUT hello.txt
  COMMAND touch hello.txt
  DEPENDS hello.txt
)

I tried running:

cmake .  
make

And hello.txt was not generated. What have I done wrong?

Answer 1

Add the following:

add_custom_target(run ALL
    DEPENDS hello.txt)

If you're familiar with makefiles, this means:

all: run
run: hello.txt