use strict;
use warnings;
use POSIX qw/getpgrp tcgetpgrp/;
if (!open(TTY, "/dev/tty")) {
    print "no tty\n";
} else {
    my $tpgrp = tcgetpgrp(fileno(*TTY));
    my $pgrp = getpgrp();
    if ($tpgrp == $pgrp) {
        print "foreground\n";
    } else {
        print "background\n";
    }
}