cmake - what does double quotes mean

Question

In code below is from a CMakeLists.txt file. It builds and installs a library that uses cmake also. My question is what is the difference between BINARY_DIR AND CONFIGURE_COMMAND, one uses double quotes and the other does not?

ExternalProject_Add(simple_amqp
  GIT_REPOSITORY    https://github.com/alanxz/SimpleAmqpClient.git
  GIT_TAG           master
  SOURCE_DIR        "${CMAKE_BINARY_DIR}/simpleamqp-src"
  BINARY_DIR        "${CMAKE_BINARY_DIR}/simpleamqp-build"
  CONFIGURE_COMMAND ${CMAKE_EXE} ../simpleamqp-src 
  BUILD_COMMAND     ${MAKE_EXE} -j4
  INSTALL_COMMAND   sudo ${MAKE_EXE} install
  TEST_COMMAND      ""
)

Possible duplicate of [cmake: when to quote variables?](https://stackoverflow.com/questions/35847655/cmake-when-to-quote-variables) — AMA, Jun 06 '18 at 13:25

score 3 · Answer 1 · answered Jun 06 '18 at 13:25

Double quotes serve to escape certain special characters in CMake, primarily the semi-colon. In CMake, the semi-colon acts as an argument separator even if it is produced by an expansion of a variable. In the (unlikely) case that the variable CMAKE_BINARY_DIR contains a semi-colon, ${CMAKE_BINARY_DIR}/simpleamqp-src would be treated as two arguments, while "${CMAKE_BINARY_DIR}/simpleamqp-src" will be a single argument.

However, given that CMake's language is somewhat obscure and esoteric at times, it's perfectly possible the real explanation is closer to "some lines were copy-pasted from code which used quotes, and some were written by someone who thought they were [not] required, and ..."

To learn more about CMake syntax, quoting, and escaping, you can read its docs, particularly the section about quoted arguments.

cmake - what does double quotes mean

1 Answers1