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
       $

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)