CMake set environment variable

Question

According to the CMake documentation

https://cmake.org/cmake/help/v3.3/command/set.html

One can do

set(ENV{<variable>} <value>)

but this gives the result

set(ENV{FOO} foo)
message("variable is $ENV{FOO}")

at configure time

variable is foo

But at Linux command

echo $FOO

the variable is not set.

EDIT:

Here's a partial solution to the problem, which was to set $PATH, so that a user has CMAKE_INSTALL_PREFIX listed first

set(file_sh ${CMAKE_CURRENT_BINARY_DIR}/path.sh)
set(path "${CMAKE_INSTALL_PREFIX}:$ENV{PATH}")
file(WRITE ${file_sh} "#!/usr/bin/env bash\n")
file(APPEND ${file_sh} "export PATH=\"${path}\"")
execute_process(COMMAND chmod a+x ${file_sh} RESULT_VARIABLE res)

this creates this file

#!/usr/bin/env bash
export PATH="/install/prefix/path:/other/path"

that later can be executed on a bash terminal with

source path.sh

Possible duplicate of [How to modify environment variables passed to custom CMake target?](https://stackoverflow.com/questions/35029277/how-to-modify-environment-variables-passed-to-custom-cmake-target) — Florian, Sep 17 '17 at 19:12
After running `cmake`? You can't change parent (bash) environment from a child process. — arrowd, Sep 18 '17 at 05:44

score 0 · Answer 1 · answered Sep 17 '17 at 18:55

0

The last paragraph of the documentation you cited gives the answer:

Set the current process environment <variable> to the given value.

It influences the current process environment that is created when CMake is started from the shell. It is not the environment of the shell itself.

answered Sep 17 '17 at 18:55

vre

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3

ok , but the paragraph title says **Set Environment Variable** The Cmake documentation is not the best I've found – Pedro Vicente Sep 17 '17 at 22:25
1

I understand your complains about the documentation, but how the environment is provided to the process is operation system specific and similar in Unix/Linux and Windows. Every process (e.g. your bash) that creates a child process (your cmake) provides the newly process a copy of its environment. You cannot change the environment of the parent process later. But you can start a intermediate process that sets the environment variables and then starts cmake. – vre Sep 19 '17 at 17:50

score 0 · Answer 2 · answered Nov 13 '20 at 14:57

Prefix your command with cmake -E env XXX=YYY.

To test, use cmake -E env XXX=YYY cmake -E environment.

This command appears to be available since CMake 3.1. For more info see https://cmake.org/cmake/help/latest/manual/cmake.1.html#run-a-command-line-tool.

CMake set environment variable

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