STDBUF(1) General Commands Manual STDBUF(1)

stdbuf — change standard streams initial buffering

stdbuf [-e bufdef] [-i bufdef] [-o bufdef] [command [...]]

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:

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

The buffer style and size is defined as follows:

"0"
unbuffered
"L"
line buffered
"B"
fully buffered with the default buffer size
size
fully buffered with a buffer of size bytes (suffixes 'k' and 'M' 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 iostat(8)'s output will not stall until the full buffer fills.

# iostat 1 | stdbuf -o L awk '$2 > 1 || $5 > 1' | cat -n

setvbuf(3)

The stdbuf utility first appeared in FreeBSD 8.4.

The original idea of the stdbuf command comes from Padraig Brady who implemented it in the GNU coreutils. Jeremie Le Hen implemented it on FreeBSD.

June 29, 2023 macOS 26.4