Using execute_process when one of the arguments contains a space

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1

There is already an entry with a similar title to what I’m trying to do, but I’m afraid it doesn’t quite answer my question.

The situation is this: I’m trying to invoke execute_process where one of the arguments contains a space. Specifically, I want to run bison with a set of flags which are specified in a string variable. For example,

execute_process(COMMAND win_flex_bison3-latest/win_bison.exe ${flags} -d  -o ${nativeGenPath} ${nativeBisonFile}
                COMMAND_ECHO STDOUT)

…where ‘flags’ may be an empty string, or it may be a sequence of space-separated flags such as “-y -v”.

The exact content of ‘flags’ is supplied by the user at build time (and the file containing this command is generated at build time using ‘configure_file’ and then ‘add_custom_target’), so I need to be able to handle various different cases.

What I find is that, if ‘flags’ is empty, of if it contains a single flag such as “-y”, then everything works. But if ‘flags’ is “-y -v” then here is the output that I see:

'win_bison.exe' '-y -v' '-d' '-o' 'C:\Users\name\Development\git\build\solutions\product\GENERATED\mathparse\parser\CalcParser.cpp' 'C:\Users\name\Development\git\apps\product\src\mathparse\parser\CalcParser.y'

C:/Users/name/Development/win_flex_bison3-latest/win_bison.exe: invalid option -- ' '

…indicating that it’s the embedded space between ‘-y’ and ‘v’ that’s the problem.

I’ve tried:

  • The above, but putting ‘flags’ in quotes, i.e. “${flags}”

  • putting the whole command line in quotes, i.e.

set(cmdstring "win_flex_bison3-latest/win_bison.exe ${flags} -d  -o ${nativeGenPath} ${nativeBisonFile}")
execute_process(COMMAND ${cmdstring}
                COMMAND_ECHO STDOUT)
  • recasting ‘flags’ as a list, i.e.
set(flags )
list(APPEND flags "-y")
list(APPEND flags "-v")

…but that just changes the error message to “invalid option – ’ ;'”

So I’m afraid I’ve run out of ideas. Is there any way of handling this situation?

2

I think you’re on the right track with the list(APPEND flags) strategy, but you also tried quoting things. How about:

set(flags -y -v) # or build up using `list(APPEND)`
execute_process(COMMAND win_flex_bison3-latest/win_bison.exe ${flags} -d  -o ${nativeGenPath} ${nativeBisonFile}
                COMMAND_ECHO STDOUT)
3

Well, blow me down… Yes, that worked. The one permutation I hadn’t tried! I was thrown by the fact that the usual recommendation when passing lists is to enclose them in quotes, but clearly this is an exception to that rule.

Thank you.

4

My rule is to quote everything except:

  • when quoting would interfere with automatic dereferencing in conditionals
  • when passing a list of built-up arguments to a command

There are exceptions like when one needs to smuggle lists with empty arguments through “higher-order” commands like ExternalProject_add.

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