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       unbuffer - unbuffer output


       unbuffer program [ args ]


       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

       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


       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
       xxxabc defxxx
       $ cat /tmp/abcdef.log | unbuffer grep abc | cat
       $ (cat /tmp/abcdef.log ; sleep 1) | unbuffer grep abc | cat
       xxxabc defxxx


       The man page is longer than the program.


       "Exploring  Expect:  A  Tcl-Based  Toolkit  for  Automating Interactive
       Programs" by Don Libes, O’Reilly and Associates, January 1995.


       Don Libes, National Institute of Standards and Technology

                                  1 June 1994                      UNBUFFER(1)