Problem exporting environment variable in Makefile - docker

Question

I would like to export the environment variable in the Makefile. In this case, is to get the IP for debugging with docker
Makefile
start:
export XDEBUG_REMOTE_HOST=$$(/sbin/ip route|awk '/kernel.*metric/ { print $$9 }') \
; docker-compose up -d
Update from answers:
version: '3.5'
services:
php:
build:
context: .
dockerfile: docker/php/Dockerfile
environment:
- XDEBUG_CONFIG="idekey=docker"
- XDEBUG_REMOTE_HOST=${XDEBUG_REMOTE_HOST}
output:
$ make start
export XDEBUG_REMOTE_HOST=$(/sbin/ip route|awk '/kernel.*metric/ { print $9 }') \
; docker-compose up -d
Starting service_php ... done
$ docker-compose exec php bash
WARNING: The XDEBUG_REMOTE_HOST variable is not set. Defaulting to a blank string.

Answer 1

You need to make sure the variable assignment and the docker command run in the same shell. Trivially, put them in the same rule:
start:
XDEBUG_REMOTE_HOST=$$(/sbin/ip route|awk '/kernel.*metric/ { print $$9 }') \
docker-compose up -d
I took out the # because it's probably simply a bad idea, especially if you need to understand what's going on here. You can use make -s once your Makefile is properly tested if you don't want to see what it's doing.
The purpose of export is to expose a variable to subprocesses, but that's not necessary here. Instead, we use the shell's general
variable=value anothervar=anothervalue command
syntax to set the value of a variable for the duration of a single command.
If the internals of docker-compose require the variable to be exported, then of course, you can do that too:
start:
export XDEBUG_REMOTE_HOST=$$(/sbin/ip route|awk '/kernel.*metric/ { print $$9 }') \
; docker-compose up -d
Notice how the backslash at the end of the first line of the command list joins the two commands on a single logical line, so they get passed to the same shell instance, and the ; command separator is required to terminate the first command. (I put the semicolon at beginning of line as an ugly reminder to the reader that this is all one command line.)
Specifically for docker-compose, the customary way to set a variable from the command line is with a specific named option;
start:
docker-compose up -e XDEBUG_REMOTE_HOST=$$(/sbin/ip route|awk '/kernel.*metric/ { print $$9 }') -d
There are other ways to solve this such as the GNU Make .ONESHELL directive but this is simple and straightforward, and portable to any Make.

Answer 2

If you assume that the route exists when make is first invoked, you can assign a make variable as opposed to a shell variable as follows:
export XDRH_MAKE_VAR:=$(shell /sbin/ip route|awk '/kernel.*metric/ { print $$9 }')
start:
#echo XDHR_MAKE_VAR=$(XDRH_MAKE_VAR)
XDEBUG_REMOTE_HOST=$(XDRH_MAKE_VAR) docker-compose up -d
XDRH_FILE:
echo $(XDRH_MAKE_VAR) > $#
someother_target:
XDEBUG_REMOTE_HOST=$(XDRH_MAKE_VAR) some_other_command
command_that_uses_it_as_param $(XDRH_MAKE_VAR)
NOTE_does_not_work:
XDEBUG_REMOTE_HOST=$(XDRH_MAKE_VAR) echo $$XDEBUG_REMOTE_HOST
The last one does not work, because the bash shell will expand $XDEBUG_REMOTE_HOST before assigning it (See here). Also, the variable is set at make parse time, so if any of your rules effect the route, then this will not be reflected in its value.
If you want to access the value in the shell afterwards, you would want to do something like:
bash> make start XDRH_FILE
bash> XDEBUG_REMOTE_HOST=`cat XDRH_FILE`
bash> docker-compose exec php bash