
Jasmine
Administrator
Jan 26, 2001, 10:38 AM
Post #1 of 1
(3475 views)
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How can I tell if there's a character waiting on a
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Can't Post
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(From the Perl FAQ) How can I tell if there's a character waiting on a filehandle? The very first thing you should do is look into getting the Term::ReadKey extension from CPAN. It now even has limited support for closed, proprietary (read: not open systems, not POSIX, not Unix, etc) systems. You should also check out the Frequently Asked Questions list in comp.unix.* for things like this: the answer is essentially the same. It's very system dependent. Here's one solution that works on BSD systems: sub key_ready { my($rin, $nfd); vec($rin, fileno(STDIN), 1) = 1; return $nfd = select($rin,undef,undef,0); } If you want to find out how many characters are waiting, there's also the FIONREAD ioctl call to be looked at. The h2ph tool that comes with Perl tries to convert C include files to Perl code, which can be required. FIONREAD ends up defined as a function in the sys/ioctl.ph file: require 'sys/ioctl.ph'; $size = pack("L", 0); ioctl(FH, FIONREAD(), $size) or die "Couldn't call ioctl: $!\n"; $size = unpack("L", $size); If h2ph wasn't installed or doesn't work for you, you can grep the include files by hand: % grep FIONREAD /usr/include/*/* /usr/include/asm/ioctls.h:#define FIONREAD 0x541B Or write a small C program using the editor of champions: % cat > fionread.c #include <sys/ioctl.h> main() { printf("%#08x\n", FIONREAD); } ^D % cc -o fionread fionread % ./fionread 0x4004667f And then hard-code it, leaving porting as an exercise to your successor. $FIONREAD = 0x4004667f; # XXX: opsys dependent $size = pack("L", 0); ioctl(FH, $FIONREAD, $size) or die "Couldn't call ioctl: $!\n"; $size = unpack("L", $size); FIONREAD requires a filehandle connected to a stream, meaning sockets, pipes, and tty devices work, but not files.
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