unbuffer Man page

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
solution, workarounds or hand-coded Expect may be more suitable. For
example, the following example shows how to allow grep to finish pro‐
cessing 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)

Ils en parlent aussi

How To: Write Custom Redirector or Rewritor Plugin For Squid in …