[CMake] EXEC_PROGRAM vs.. EXECUTE_PROCESS problem

[Brad King]

Alexander Neundorf wrote:
> EXECUTE_PROCESS(COMMAND ${RUBY_EXECUTABLE} -r rbconfig -e 'puts Config::CONFIG["libdir"]'
>    OUTPUT_VARIABLE RUBY_POSSIBLE_LIB_PATH)

EXECUTE_PROCESS does not use a shell like EXEC_PROGRAM so it directly
converts CMake arguments into command line arguments.  The above gives
ruby the command line

[ruby]
[-r]
[rbconfig]
[-e]
['puts]
[Config::CONFIG["libdir"]']

because '' is not a string delimeter for the CMake language.  Ruby
complains about the unterminated string because it is getting the script
"'puts".  Convert the call to pass a CMake argument with the full script:

EXECUTE_PROCESS(
  COMMAND ${RUBY_EXECUTABLE} -r rbconfig
          -e "puts Config::CONFIG['libdir']"
  OUTPUT_VARIABLE RUBY_POSSIBLE_LIB_PATH
  )

> EXEC_PROGRAM(${RUBY_EXECUTABLE} ARGS -r rbconfig -e 'puts
Config::CONFIG[\"archdir\"]'
>   OUTPUT_VARIABLE RUBY_ARCH_DIR)

This version works because all the arguments are appended together
separated by whitespace and then passed to a shell.  The '' delimeters
work in that shell.  This will probably not work on Windows though.

-Brad