UNBUFFER(1) General Commands Manual UNBUFFER(1)
NAME
unbuffer - unbuffer output
SYNOPSIS
unbuffer program [ args ]
INTRODUCTION
unbuffer disables the output buffering that occurs when program output
is redirected from non-interactive programs. For example, suppose you
are watching the output from a fifo by running it through od and then
more.
od -c /tmp/fifo | more
You will not see anything until a full page of output has been pro-
duced.
You can disable this automatic buffering as follows:
unbuffer od -c /tmp/fifo | more
Normally, unbuffer does not read from stdin. This simplifies use of
unbuffer in some situations. To use unbuffer in a pipeline, use the -p
flag. Example:
process1 | unbuffer -p process2 | process3
CAVEATS
unbuffer -p may appear to work incorrectly if a process feeding input
to unbuffer exits. Consider:
process1 | unbuffer -p process2 | process3
If process1 exits, process2 may not yet have finished. It is impossi-
ble for unbuffer to know long to wait for process2 and process2 may not
ever finish, for example, if it is a filter. For expediency, unbuffer
simply exits when it encounters an EOF from either its input or
process2.
In order to have a version of unbuffer that worked in all situations,
an oracle would be necessary. If you want an application-specific so-
lution, workarounds or hand-coded Expect may be more suitable. For ex-
ample, the following example shows how to allow grep to finish process-
ing when the cat before it finishes first. Using cat to feed grep
would never require unbuffer in real life. It is merely a placeholder
for some imaginary process that may or may not finish. Similarly, the
final cat at the end of the pipeline is also a placeholder for another
process.
$ cat /tmp/abcdef.log | grep abc | cat
abcdef
xxxabc defxxx
$ cat /tmp/abcdef.log | unbuffer grep abc | cat
$ (cat /tmp/abcdef.log ; sleep 1) | unbuffer grep abc | cat
abcdef
xxxabc defxxx
$
BUGS
The man page is longer than the program.
SEE ALSO
"Exploring Expect: A Tcl-Based Toolkit for Automating Interactive Pro-
grams" by Don Libes, O'Reilly and Associates, January 1995.
AUTHOR
Don Libes, National Institute of Standards and Technology
1 June 1994 UNBUFFER(1)
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