expect_unbuffer - Online in the Cloud

PROGRAM:

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 produced.

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 impossible 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 processing 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
$

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