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)