macro(LOG line)
   message(STATUS ${line})
   file(APPEND ${CMAKE_CURRENT_BINARY_DIR}/AbsPathTest.txt "${line}\n")
endmacro(LOG line)

file(WRITE ${CMAKE_CURRENT_BINARY_DIR}/AbsPathTest.txt "test\n")

set(path1 "/abs/unix")
set(path2 "../rel")
set(path3 ${CMAKE_ROOT})

message(STATUS "dos: ${path3}")

macro(GET_ABS_PATH _abs_filename _filename)
     IF(${_filename} MATCHES "^/.+")
        SET(${_abs_filename} ${_filename})
     ELSE(${_filename} MATCHES "^/.+")
        IF(${_filename} MATCHES "^[a-zA-Z]:\\\\")
           SET(${_abs_filename} ${_filename})
        ELSE(${_filename} MATCHES "^[a-zA-Z]:\\\\")
           SET(${_abs_filename} ${CMAKE_CURRENT_SOURCE_DIR}/${_filename})
        ENDIF(${_filename} MATCHES "^[a-zA-Z]:\\\\")
     ENDIF(${_filename} MATCHES "^/.+")
endmacro(GET_ABS_PATH)


get_abs_path(abs ${path1})
log(${path1})
log(${abs})

get_abs_path(abs ${path2})
log(${path2})
log(${abs})

get_abs_path(abs "${path3}")
log(${path3})
log(${abs})