Read environment variables from file in Windows Batch (cmd.exe)

Question

I'm trying to read variables from a batch file for later use in the batch script, which is a Java launcher. I'd ideally like to have the same format for the settings file on all platforms (Unix, Windows), and also be a valid Java Properties file. That is, it should look like this:

setting1=Value1
setting2=Value2
...

Is it possible to read such values like you would in a Unix shell script? The could should look something like this:

READ settingsfile.xy
java -Dsetting1=%setting1% ...

I know that this is probably possible with SET setting1=Value1, but I'd really rather have the same file format for the settings on all platforms.

To clarify: I need to do this in the command line/batch environment as I also need to set parameters that cannot be altered from within the JVM, like -Xmx or -classpath.

Answer 1

You can do this in a batch file as follows:

setlocal
FOR /F "tokens=*" %%i in ('type Settings.txt') do SET %%i
java -Dsetting1=%setting1% ...
endlocal

This reads a text file containing strings like "SETTING1=VALUE1" and calls SET to set them as environment variables.

setlocal/endlocal are used to limit the scope of the environment variables to the execution of your batch file.

The CMD Command Processor is actually quite powerful, though with a rather byzantine syntax.

Answer 2

You can pass the property file as a parameter to a Java program (that may launch the main program later on). And then benefit from the multi platform paradigm.

Answer 3

It may be wise to only import specific variables from a properties file (ones you know about ahead of time), in that case I recommend a function like the following:

:parsePropertiesFile
    set PROPS_FILE=%1
    shift
    :propLoop
    if "%1"=="" goto:eof
    FOR /F "tokens=*" %%i in ('type %PROPS_FILE% ^| findStr.exe "%1="') do SET %%i
    shift
    GOTO propLoop
goto:eof

Which would be called by call:parsePropertiesFile props.properties setting1 setting2 to set the variables setting1 and setting2

Answer 4

You can also access the OS' environment variables from within a Java program:

import java.util.Map;

public class EnvMap {
    public static void main (String[] args) {
        Map<String, String> env = System.getenv();
        for (String envName : env.keySet()) {
            System.out.format("%s=%s%n", envName, env.get(envName));
        }
    }
}