How to make output of any shell command unbuffered?

Question

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 solution how to make any command unbuffered?

Thanks, Boda Cydo.

Answer 1

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.

Answer 2

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

Example usage:

unbuffer hexdump file | ./my_script