Manual Pages  — STDBUF

stdbuf is used to change the initial buffering of standard input, standard output and/or standard error streams for command. It relies on libstdbuf(3) which is loaded and configured by stdbuf through environment variables.

The options are as follows:

-e bufdef
	Set initial buffering of the standard error stream for command as defined by bufdef (see Sx BUFFER DEFINITION).
-i bufdef
	Set initial buffering of the standard input stream for command as defined by bufdef (see Sx BUFFER DEFINITION).
-o bufdef
	Set initial buffering of the standard output stream for command as defined by bufdef (see Sx BUFFER DEFINITION).

Buffer definition is the same as in libstdbuf(3):

"0"	unbuffered
"L"	line buffered
"B"	fully buffered with the default buffer size
size	fully buffered with a buffer of size bytes (suffixes 'k', 'M' and 'G' are accepted)

In the following example, the stdout stream of the awk(1) command will be fully buffered by default because it does not refer to a terminal. stdbuf is used to force it to be line-buffered so vmstat(8)'s output will not stall until the full buffer fills.

# vmstat 1 | stdbuf -o L awk '$2 > 1 || $3 > 1' | cat -n

libstdbuf(3), setvbuf(3)