STDBUF

Section: User Commands (1)
Updated: February 2026
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NAME

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

SYNOPSIS

stdbuf ,OPTION/... ,COMMAND/  

DESCRIPTION

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

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

X'tty: link https://www.gnu.org/software/coreutils/manual/coreutils.html#stdbu-i'-i, --input=,MODEX'tty: link'/

adjust standard input stream buffering

X'tty: link https://www.gnu.org/software/coreutils/manual/coreutils.html#stdbu-o'-o, --output=,MODEX'tty: link'/

adjust standard output stream buffering

X'tty: link https://www.gnu.org/software/coreutils/manual/coreutils.html#stdbu-e'-e, --error=,MODEX'tty: link'/

adjust standard error stream buffering

X'tty: link https://www.gnu.org/software/coreutils/stdbuf#stdbu-help'--helpX'tty: link'

display this help and exit

X'tty: link https://www.gnu.org/software/coreutils/stdbuf#stdbu-version'--versionX'tty: link'

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

 

EXAMPLES

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

BUGS

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

AUTHOR

Written by Padraig Brady.  

REPORTING BUGS

Report bugs to: bug-coreutils@gnu.org

Report Gentoo bugs to: https://bugs.gentoo.org/
GNU coreutils home page: <https://www.gnu.org/software/coreutils/>
General help using GNU software: <https://www.gnu.org/gethelp/>
Report any translation bugs to <https://translationproject.org/team/>  

SEE ALSO

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

Packaged by Gentoo (9.10 (p0))
Copyright © 2026 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.

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Index

NAME

SYNOPSIS

DESCRIPTION

Exit status:

EXAMPLES

BUGS

AUTHOR

REPORTING BUGS

SEE ALSO