CMake quote escape conumdrum

Question

I just don't seem to be able to wrap my head around CMake's escape rules. Given:

set(X A B C)
add_custom_target( works COMMAND DUMMY=0 X="${X}" env | grep ^X= COMMENT "This works")
add_custom_target( fails COMMAND X="${X}" env | grep ^X= COMMENT "This fails")

The intention is to execute command X="A B C" env. The custom target works correctly constructs the command, where as fails incorrectly executes:

X=\"A B C\" env ...

But why?

Answer 1

Actually you ran into two problems:

1. Don't quote CMake variables in custom commands. CMake will do the necessary escape sequences for you.
2. The first literal after COMMAND is assumed to be a command name or file. So CMake tries to handle it as a single "string".

So I changed the quoting and the env call and the following did work for me:

cmake_minimum_required(VERSION 2.8)

project(QuotedStrings)

set(X "A B C")
add_custom_target( works COMMAND env DUMMY=0 X=${X} | grep ^X= COMMENT "This works")
add_custom_target( fails_no_more COMMAND env X=${X} | grep ^X= COMMENT "This works too")

For more details and possibilities see:

• cmake: How to include literal double-quote in custom command?
• cmake: when to quote variables?