man pages section 1: User Commands

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Updated: July 2014

unbuffer (1)


unbuffer - unbuffer output


unbuffer program [ args ]


User Commands                                         UNBUFFER(1)

     unbuffer - unbuffer output

     unbuffer program [ args ]

     unbuffer disables the output buffering that occurs when pro-
     gram 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 simpli-
     fies 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

SunOS 5.11           Last change: 1 June 1994                   1

User Commands                                         UNBUFFER(1)

     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.

     See   attributes(5)   for   descriptions  of  the  following

     |Availability   | shell/expect     |
     |Stability      | Uncommitted      |
     "Exploring Expect: A Tcl-Based Toolkit for Automating Inter-
     active Programs" by Don Libes, O'Reilly and Associates, Jan-
     uary 1995.

     Don Libes, National Institute of Standards and Technology

     This  software  was   built   from   source   available   at    The  original
     community  source  was   downloaded   from    http://source-

     Further information about this software can be found on  the
     open source community website at

SunOS 5.11           Last change: 1 June 1994                   2