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Re: Testing for the existence of STDIN?

by wog (Curate)
on Jan 24, 2002 at 03:22 UTC ( #141064=note: print w/replies, xml ) Need Help??

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.)

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