How do I include a literal double quote in a custom CMake command?

问题

I'm trying to create a custom command that runs with some environment variables, such as LDFLAGS, whose value needs to be quoted if it contains spaces:

LDFLAGS="-Lmydir -Lmyotherdir"

I cannot find a way to include this argument in a CMake custom command, due to CMake's escaping rules. Here's what I've tried so far:

COMMAND LDFLAGS="-Ldir -Ldir2" echo blah VERBATIM)

yields "LDFLAGS=\"-Ldir -Ldir2\"" echo blah

COMMAND LDFLAGS=\"-Ldir -Ldir2\" echo blah VERBATIM)

yields LDFLAGS=\"-Ldir -Ldir2\" echo blah

It seems I either get the whole string quoted, or the escaped quotes don't resolve when used as part of the command.

I would appreciate either a way to include the literal double-quote or as an alternative a better way to set environment variables for a command. Please note that I'm still on CMake 2.8, so I don't have the new "env" command available in 3.2.

Note that this is not a duplicate of When to quote variables? as none of those quoting methods work for this particular case.

回答1:

The obvious choice - often recommended when hitting the boundaries of COMMAND especially with older versions of CMake - is to use an external script.

I just wanted to add some simple COMMAND only variations that do work and won't need a shell, but are - I have to admit - still partly platform dependent.

One example would be to put only the quoted part into a variable:

set(vars_as_string "-Ldir -Ldir2")
add_custom_target(
    QuotedEnvVar
    COMMAND env LD_FLAGS=${vars_as_string} | grep LD_FLAGS
)

Which actually does escape the space and not the quotes.

Another example would be to add it with escaped quotes as a "launcher" rule:

add_custom_target(
    LauncherEnvVar
    COMMAND env | grep LD_FLAGS
)
set_target_properties(
    LauncherEnvVar 
    PROPERTIES RULE_LAUNCH_CUSTOM "env LD_FLAGS=\"-Ldir -Ldir2\""
)

Edit: Added examples for multiple quoted arguments without the need of escaping quotes

Another example would be to "hide some of the complexity" in a function and - if you want to add this to all your custom command calls - use the global/directory RULE_LAUNCH_CUSTOM property:

function(set_env)
    get_property(_env GLOBAL PROPERTY RULE_LAUNCH_CUSTOM)
    if (NOT _env)
        set_property(GLOBAL PROPERTY RULE_LAUNCH_CUSTOM "env")
    endif()
    foreach(_arg IN LISTS ARGN)
        set_property(GLOBAL APPEND_STRING PROPERTY RULE_LAUNCH_CUSTOM " ${_arg}")
    endforeach()
endfunction(set_env)

set_env(LDFLAGS="-Ldir1 -Ldir2" CFLAGS="-Idira -Idirb")

add_custom_target(
    MultipleEnvVar
    COMMAND env | grep -E 'LDFLAGS|CFLAGS'
)

Alternative (for CMake >= 3.0)

I think what we actually are looking for here (besides the cmake -E env ...) is named Bracket Argument and does allow any character without the need of adding backslashes:

set_property(
    GLOBAL PROPERTY 
        RULE_LAUNCH_CUSTOM [=[env LDFLAGS="-Ldir1 -Ldir2" CFLAGS="-Idira -Idirb"]=]
)
add_custom_target(
    MultipleEnvVarNew
    COMMAND env | grep -E 'LDFLAGS|CFLAGS'
)

References

0005145: Set environment variables for ADD_CUSTOM_COMMAND/ADD_CUSTOM_TARGET
How to modify environment variables passed to custom CMake target?
[CMake] How to set environment variable for custom command
cmake: when to quote variables?

回答2:

Ok, I removed my original answer as the one proposed by @Florian is better. There is one additional tweak needed for multiple quoted args. Consider a list of environment variables as such:

set(my_env_vars LDFLAGS="-Ldir1 -Ldir2" CFLAGS="-Idira -Idirb")

In order to produce the desired expansion, convert to string and then replace ; with a space.

set(my_env_string "${my_env_vars}") #produces LDFLAGS="...";CFLAGS="..."
string(REPLACE ";" " " my_env_string "${my_env_string}")

Then you can proceed with @Florian's brilliant answer and add the custom launch rule. If you need semicolons in your string then you'll need to convert them to something else first.

Note that in this case I didn't need to launch with env:

set_target_properties(mytarget PROPERTIES RULE_LAUNCH_CUSTOM "${my_env_string}")

This of course depends on your shell.

On second thought, my original answer is below as I also have a case where I don't have access to the target name.

set(my_env LDFLAGS=\"-Ldir -Ldir2" CFLAGS=\"-Idira -Idirb\")
add_custom_command(COMMAND sh -c "${my_env} grep LDFLAGS" VERBATIM)

This technique still requires that the semicolons from the list->string conversion be replaced.

来源：https://stackoverflow.com/questions/39368525/how-do-i-include-a-literal-double-quote-in-a-custom-cmake-command

标签

cmake

escaping

quotes

literals