I'm reading from a serial port connected to a gps device sending nmea strings. A simplified invocation to illustrate my point:  $ awk '{ print $0 }' /dev/ttyPSC9   GPGGA,073651.000,6310.1043,N,01436.1539,E,1,07,1.0,340.2,M,33.3,M,,0000*56  $GPGSA,A,3,28,22,09,27,01,19,17,,,,,,2.3,1.0,2.0*39  $GPRMC,073651.000,A,6310.1043,N,01436.1539,E,0.42,163.42,070312,,,A*67  GPGGA,073652.000,6310.1043,N,01436.1540,E,1,07,1.0,339.2,M,33.3,M,,0000*55  $GPGSA,A,3,28,22,09,27,01,19,17,,,,,,2.3,1.0,2.0*39If I instead try to read from a pipe, awk buffers the input before sending it to stdout.$ cat /dev/ttyPSC9 | awk '{ print $0 }'<long pause>GPGGA,073651.000,6310.1043,N,01436.1539,E,1,07,1.0,340.2,M,33.3,M,,0000*56$GPGSA,A,3,28,22,09,27,01,19,17,,,,,,2.3,1.0,2.0*39$GPRMC,073651.000,A,6310.1043,N,01436.1539,E,0.42,163.42,070312,,,A*67GPGGA,073652.000,6310.1043,N,01436.1540,E,1,07,1.0,339.2,M,33.3,M,,0000*55$GPGSA,A,3,28,22,09,27,01,19,17,,,,,,2.3,1.0,2.0*39How can I avoid the buffering?Edit: Kyle Jones suggested that cat is buffering it's output but that doesn't appear to be happening:$ strace cat /dev/ttyPSC9 | awk '{ print $0 }'write(1, 2,..., 2)                    = 2read(3, E..., 4096)                   = 1write(1, E..., 1)                     = 1read(3, ,0..., 4096)                  = 2When I think about it: I thought that a program used line buffering when writing to a terminal and regular buffering for all other cases. Then, why is cat not buffering more? Is the serial port signaling EOF? Then why is cat not terminated?
Why does awk do full buffering when reading from a pipe
awk;tty;serial port
It is likely to be buffering in awk, not cat. In the first case, awk believes it is interactive because its input and output are TTYs (even though they're different TTYs - I'm guessing that awk is not checking that). In the second, the input is a pipe so it runs non-interactively.You will need to explicitly flush in your awk program. This is not portable, though.For more background and details on how to flush output, read: http://www.gnu.org/software/gawk/manual/html_node/I_002fO-Functions.html