[CMake] Please update the documentation for execute_process

[Andreas Naumann]

Am 25.08.2017 um 16:12 schrieb Jeffrey Walton:
>> Below is a typical case for us
>> (https://github.com/weidai11/cryptopp/blob/master/CMakeLists.txt). If
>> it looks pretty shitty, it probably is. That's the best we have been
>> able to come up with based on the documentation.
> Below is the example code. We don't know whether it should be:
>
> set(SHELL_CMD sh)
> set(SHELL_ARGS -c)
> set(GREP_CMD egrep)
> set(GREP_ARGS -i -c)
>
> execute_process(COMMAND ${SHELL_CMD} ${SHELL_ARGS}
> "${CMAKE_CXX_COMPILER} -dumpmachine 2>&1"
> COMMAND ${GREP_CMD} ${GREP_ARGS} "amd64"
> OUTPUT_VARIABLE CRYPTOPP_AMD64
> OUTPUT_STRIP_TRAILING_WHITESPACE)
>
> Or:
>
> COMMAND "${SHELL_CMD}", "${CMAKE_CXX_COMPILER}", "-dumpmachine", "2>&1"
>
> Or:
>
> COMMAND "${SHELL_CMD}" "${CMAKE_CXX_COMPILER}" "-dumpmachine" "2>&1"
>
> Or:
>
> set(SHELL_CMD sh)
> set(GREP_CMD egrep)
>
> execute_process(COMMAND ${SHELL_CMD} "-c" "${CMAKE_CXX_COMPILER}
> "-dumpmachine" "2>&1"
> COMMAND ${GREP_CMD} ${GREP_ARGS} "-i" "-c" "amd64"
> OUTPUT_VARIABLE CRYPTOPP_AMD64
> OUTPUT_STRIP_TRAILING_WHITESPACE)
>
> And we certainly don't know what to do with "2>&1" because there is no example.
The documentation states
"If OUTPUT_VARIABLE or ERROR_VARIABLE are given the variable named will 
be set with the contents of the standard output and standard error pipes 
respectively. If the same variable is named for both pipes their output 
will be merged in the order produced

so I would suspect to use something like

execute_process(COMMAND "${CMAKE_CXX_COMPILER}"
"-dumpmachine" OUTPUT_VARIABLE output_dump ERROR_VARIABLE output_dump)

and then use a
if( output_dump MATCHES "amd64" )
..

endif()

block

Does that work?
>
> Jeff
>
> **********
>
> set(SHELL_CMD sh -c)
> set(GREP_CMD egrep -i -c)
>
> execute_process(COMMAND ${SHELL_CMD} "${CMAKE_CXX_COMPILER} -dumpmachine 2>&1"
> COMMAND ${GREP_CMD} "amd64"
> OUTPUT_VARIABLE CRYPTOPP_AMD64
> OUTPUT_STRIP_TRAILING_WHITESPACE)
>
> execute_process(COMMAND ${SHELL_CMD} "${CMAKE_CXX_COMPILER} -dumpmachine 2>&1"
> COMMAND ${GREP_CMD} "x86_64"
> OUTPUT_VARIABLE CRYPTOPP_X86_64
> OUTPUT_STRIP_TRAILING_WHITESPACE)
>
> execute_process(COMMAND ${SHELL_CMD} "${CMAKE_CXX_COMPILER} -dumpmachine 2>&1"
> COMMAND ${GREP_CMD} "i.86"
> OUTPUT_VARIABLE CRYPTOPP_I386
> OUTPUT_STRIP_TRAILING_WHITESPACE)
>
> # http://github.com/weidai11/cryptopp/issues/466
> execute_process(COMMAND ${SHELL_CMD} "${CMAKE_CXX_COMPILER} -dumpmachine 2>&1"
> COMMAND ${GREP_CMD} "mingw32"
> OUTPUT_VARIABLE CRYPTOPP_MINGW32
> OUTPUT_STRIP_TRAILING_WHITESPACE)
>
> # http://github.com/weidai11/cryptopp/issues/466
> execute_process(COMMAND ${SHELL_CMD} "${CMAKE_CXX_COMPILER} -dumpmachine 2>&1"
> COMMAND ${GREP_CMD} "w64-mingw32"
> OUTPUT_VARIABLE CRYPTOPP_MINGW64
> OUTPUT_STRIP_TRAILING_WHITESPACE)
>
> execute_process(COMMAND ${SHELL_CMD} "${CMAKE_CXX_COMPILER} -dumpmachine 2>&1"
> COMMAND ${GREP_CMD} "x32"
> OUTPUT_VARIABLE CRYPTOPP_X32
> OUTPUT_STRIP_TRAILING_WHITESPACE)
>
> execute_process(COMMAND ${SHELL_CMD} "${CMAKE_CXX_COMPILER} -dumpmachine 2>&1"
> COMMAND ${GREP_CMD} "Aarch32"
> OUTPUT_VARIABLE CRYPTOPP_AARCH32
> OUTPUT_STRIP_TRAILING_WHITESPACE)
>
> execute_process(COMMAND ${SHELL_CMD} "${CMAKE_CXX_COMPILER} -dumpmachine 2>&1"
> COMMAND ${GREP_CMD} "Aarch64"
> OUTPUT_VARIABLE CRYPTOPP_AARCH64
> OUTPUT_STRIP_TRAILING_WHITESPACE)
>
> # http://stackoverflow.com/q/12515462/608639
> execute_process(COMMAND ${SHELL_CMD} "${CMAKE_CXX_COMPILER} -dumpmachine 2>&1"
> COMMAND ${GREP_CMD} "\\<ARM\\>"
> OUTPUT_VARIABLE CRYPTOPP_ARM
> OUTPUT_STRIP_TRAILING_WHITESPACE)
>
> execute_process(COMMAND ${SHELL_CMD} "${CMAKE_CXX_COMPILER} -dumpmachine 2>&1"
> COMMAND ${GREP_CMD} "ARMHF"
> OUTPUT_VARIABLE CRYPTOPP_ARMHF
> OUTPUT_STRIP_TRAILING_WHITESPACE)
>
> execute_process(COMMAND ${SHELL_CMD} "${CMAKE_CXX_COMPILER} -dumpmachine 2>&1"
> COMMAND ${GREP_CMD} "ARM7L"
> OUTPUT_VARIABLE CRYPTOPP_ARM7L
> OUTPUT_STRIP_TRAILING_WHITESPACE)
>
> # Fixup?
> if ("${CRYPTOPP_MINGW64}" STREQUAL "1")
> unset(CRYPTOPP_MINGW32)
> endif()
>
> # MinGW32
> if ("${CRYPTOPP_MINGW32}" STREQUAL "1")
> set(CRYPTOPP_I386 "1")
> endif()
> # OpenBSD and MinGW64
> if ("${CRYPTOPP_X86_64}" STREQUAL "1" OR "${CRYPTOPP_MINGW64}" STREQUAL "1")
> set(CRYPTOPP_AMD64 "1")
> endif()
> # arm7l is another 32-bit hard float machine. RPI-3 is arm7l on 64-bit hardware
> if ("${CRYPTOPP_ARM}" STREQUAL "1" OR "${CRYPTOPP_ARM7L}" STREQUAL "1")
> set(CRYPTOPP_ARMHF "1")
> endif()