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,R,Q. 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.

Exit status:

125

if the stdbuf command itself fails

126

if COMMAND is found but cannot be invoked

127

if COMMAND cannot be found

-

the exit status of COMMAND otherwise

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

Full documentation <https://www.gnu.org/software/coreutils/stdbuf>
or available locally via: info '(coreutils) stdbuf invocation'