UNBUFFER(1)                                           UNBUFFER(1)



NAME
       unbuffer - unbuffer output

SYNOPSIS
       unbuffer program [ args ]

INTRODUCTION
       unbuffer  disables  the  output buffering that occurs when
       program output is redirected.  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 simpli-
       fies 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 pro-
       cess2 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
       $

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  Associ-
       ates, January 1995.

AUTHOR
       Don Libes, National Institute of Standards and Technology



                           1 June 1994                UNBUFFER(1)