You can tell if STDIN is a tty or not, which isn't quite the same thing, but it might suffice: 
#!/usr/bin/perl
use POSIX qw(isatty);
if (isatty(STDIN)) {
   die("nope. not like that\n");
}
while (<>) {
   print "$_\n";
}

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In reply to Re: How do I Determine if my script is being piped to? by kschwab
in thread How do I Determine if my script is being piped to? by netguy

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