FAQ 8.37 How do I find out if I'm running interactively or not?

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8.37: How do I find out if I'm running interactively or not?

    Good question. Sometimes "-t STDIN" and "-t STDOUT" can give clues,
    sometimes not.

            if (-t STDIN && -t STDOUT) {
                    print "Now what? ";

    On POSIX systems, you can test whether your own process group matches
    the current process group of your controlling terminal as follows:

            use POSIX qw/getpgrp tcgetpgrp/;

            # Some POSIX systems, such as Linux, can be
            # without a /dev/tty at boot time.
            if (!open(TTY, "/dev/tty")) {
                    print "no tty\n";
            } else {
                    $tpgrp = tcgetpgrp(fileno(*TTY));
                    $pgrp = getpgrp();
                    if ($tpgrp == $pgrp) {
                            print "foreground\n";
                    } else {
                            print "background\n";


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