http://qs321.pair.com?node_id=141064


in reply to Testing for the existence of STDIN?

In addition to the code above, you could use the -t filetest operator to check if STDIN was opened to a terminal (and thus not a pipe, etc):

if (-t STDIN) { # we're running from a shell, without input being # piped to us. } else { # ... }
Or you could also try a non-blocking read of STDIN, which most directly answers your original question of seeing if there is any input waiting without blocking:
use IO::Handle; STDIN->blocking(0); # and try to read from it, like you would normally. my $line = <STDIN>; if (defined $line) { # we have input, read succeeded } else { # no input at the moment. }
(Note that this technique may give false negatives if pipes take some time to start writing data.)