Can a makefile update the calling environment?

Question

Is it possible to update the environment from a makefile? I want to be able to create a target to set the client environment variables for them. Something like this:

AXIS2_HOME ?= /usr/local/axis2-1.4.1
JAVA_HOME  ?= /usr/java/latest
CLASSPATH  := foo foo

setenv:
    export AXIS2_HOME
    export JAVA_HOME
    export CLASSPATH

So that the client can simply do:

make setenv all
java MainClass

and have it work without them needing to set the classpath for the java execution themselves.

Or am I looking to do this the wrong way and there is a better way?

Answer 1

No, you can't update the environment in the calling process this way. In general, a subprocess cannot modify the environment of the parent process. One notable exception is batch files on Windows, when run from a cmd shell. Based on the example you show, I guess you are not running on Windows though.

Usually, what you're trying to accomplish is done with a shell script that sets up the environment and then invokes your intended process. For example, you might write a go.sh script like this:

!#/bin/sh
AXIS2_HOME=/usr/local/axix2-1.4.1
JAVA_HOME=/usr/java/latest
CLASSPATH=foo foo
export AXIS2_HOME
export JAVA_HOME
export CLASSPATH
java MainClass

Make go.sh executable and now you can run your app as ./go.sh. You can make your script more elaborate too, if you like -- for example, you may want to make "MainClass" a parameter to the script rather than hard coding it.

Answer 2

From your question I am assuming you're using the bash shell.

You can place the variable definitions in a shell script, like so:

AXIS2_HOME=/usr/local/axis2-1.4.1
export AXIS2_HOME
#etc

And then source the script into the current environment, with

source <filename>

or just

. <filename>

That executes the script in the current shell (i.e. no child process), so any environment changes the script makes will persist.