unbuffer

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 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)