STDBUF(1) User Commands STDBUF(1)

stdbuf - Run COMMAND, with modified buffering operations for its standard streams.

stdbuf OPTION... COMMAND

Run COMMAND, with modified buffering operations for its standard streams.

Mandatory arguments to long options are mandatory for short options too.

-i, --input=MODE
adjust standard input stream buffering
-o, --output=MODE
adjust standard output stream buffering
-e, --error=MODE
adjust standard error stream buffering
--help
display this help and exit
--version
output version information and exit

If MODE is 'L' the corresponding stream will be line buffered. This option is invalid with standard input.

If MODE is '0' the corresponding stream will be unbuffered.

Otherwise MODE is a number which may be followed by one of the following: KB 1000, K 1024, MB 1000*1000, M 1024*1024, and so on for G, T, P, E, Z, Y. Binary prefixes can be used, too: KiB=K, MiB=M, and so on. In this case the corresponding stream will be fully buffered with the buffer size set to MODE bytes.

NOTE: If COMMAND adjusts the buffering of its standard streams ('tee' does for example) then that will override corresponding changes by 'stdbuf'. Also some filters (like 'dd' and 'cat' etc.) don't use streams for I/O, and are thus unaffected by 'stdbuf' settings.

tail -f access.log | stdbuf -oL cut -d ' ' -f1 | uniq
This will immediately display unique entries from access.log

On GLIBC platforms, specifying a buffer size, i.e., using fully buffered mode will result in undefined operation.

Written by Padraig Brady.

GNU coreutils online help: https://www.gnu.org/software/coreutils/
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Copyright © 2020 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later https://gnu.org/licenses/gpl.html.
This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law.

Full documentation https://www.gnu.org/software/coreutils/stdbuf
or available locally via: info '(coreutils) stdbuf invocation'
March 2020 GNU coreutils 8.32