Currently, on all platforms except MSWin32, all system calls (e.g., using system() or back-ticks) made from threads use the environment variable settings from the main thread. In other words, changes made to %ENV in a thread will not be visible in system calls made by that thread.

To work around this, set environment variables as part of the system call. For example:

    my $msg = 'hello';
    system("FOO=$msg; echo \$FOO"); # Outputs 'hello' to STDOUT

On MSWin32, each thread maintains its own set of environment variables.