man > expect_unbuffer(1)

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 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 situa‐
       tions.  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 nec‐
       essary.   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 Programs" by Don Libes,
       O'Reilly and Associates, January 1995.

AUTHOR
       Don Libes, National Institute of Standards and Technology

                                             1 June 1994                                 UNBUFFER(1)