How to make output of any shell command unbuffered?

Is there a way to run shell commands without output buffering?

For example, hexdump file | ./my_script will only pass input from hexdump to my_script in buffered chunks, not line by line.

Actually I want to know a general开发者_StackOverflow中文版 solution how to make any command unbuffered?

Try stdbuf, included in GNU coreutils and thus virtually any Linux distro. This sets the buffer length for input, output and error to zero:

stdbuf -i0 -o0 -e0 command

The command unbuffer from the expect package disables the output buffering:
Ubuntu Manpage: unbuffer - unbuffer output

Example usage:

unbuffer hexdump file | ./my_script

AFAIK, you can't do it without ugly hacks. Writing to a pipe (or reading from it) automatically turns on full buffering and there is nothing you can do about it :-(. "Line buffering" (which is what you want) is only used when reading/writing a terminal. The ugly hacks exactly do this: They connect a program to a pseudo-terminal, so that the other tools in the pipe read/write from that terminal in line buffering mode. The whole problem is described here:

• http://www.pixelbeat.org/programming/stdio_buffering/

The page has also some suggestions (the aforementioned "ugly hacks") what to do, i.e. using unbuffer or pulling some tricks with LD_PRELOAD.

You could also use the script command to make the output of hexdump line-buffered (hexdump will be run in a pseudo terminal which tricks hexdump into thinking its writing its stdout to a terminal, and not to a pipe).

# cf. http://unix.stackexchange.com/questions/25372/turn-off-buffering-in-pipe/
stty -echo -onlcr
script -q /dev/null hexdump file | ./my_script         # FreeBSD, Mac OS X
script -q -c "hexdump file" /dev/null | ./my_script    # Linux
stty echo onlcr

One should use grep or egrep "--line-buffered" options to solve this. no other tools needed.