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       tail - copy the last part of a file


       tail [-f][ -c number| -n number][file]


       The  tail  utility  shall  copy  its  input  file  to  the  standard output beginning at a
       designated place.

       Copying shall begin at the point in the file indicated by  the  -c  number  or  -n  number
       options. The option-argument number shall be counted in units of lines or bytes, according
       to the options -n and -c. Both line and byte counts start from 1.

       Tails relative to the end of the file may be saved in an internal buffer, and thus may  be
       limited in length. Such a buffer, if any, shall be no smaller than {LINE_MAX}*10 bytes.


       The  tail  utility  shall  conform to the Base Definitions volume of IEEE Std 1003.1-2001,
       Section 12.2, Utility Syntax Guidelines.

       The following options shall be supported:

       -c  number
              The application shall ensure that the number option-argument is a  decimal  integer
              whose  sign  affects  the  location  in  the  file, measured in bytes, to begin the

                                 Sign   Copying Starts
                                 +      Relative to the beginning of the file.
                                 -      Relative to the end of the file.
                                 none   Relative to the end of the file.

       The origin for counting shall be 1; that is, -c +1 represents the first byte of the  file,
       -c -1 the last.

       -f     If the input file is a regular file or if the file operand specifies a FIFO, do not
              terminate after the last line of the input file has been copied, but read and  copy
              further bytes from the input file when they become available. If no file operand is
              specified and standard input is a pipe, the -f option  shall  be  ignored.  If  the
              input  file  is not a FIFO, pipe, or regular file, it is unspecified whether or not
              the -f option shall be ignored.

       -n  number
              This option shall be equivalent to -c number, except the starting location  in  the
              file  shall be measured in lines instead of bytes. The origin for counting shall be
              1; that is, -n +1 represents the first line of the file, -n -1 the last.

       If neither -c nor -n is specified, -n 10 shall be assumed.


       The following operand shall be supported:

       file   A pathname of an input file. If no file operands are specified, the standard  input
              shall be used.


       The  standard  input  shall  be used only if no file operands are specified. See the INPUT
       FILES section.


       If the -c option is specified, the input file can contain arbitrary data;  otherwise,  the
       input file shall be a text file.


       The following environment variables shall affect the execution of tail:

       LANG   Provide  a  default  value for the internationalization variables that are unset or
              null. (See the  Base  Definitions  volume  of  IEEE Std 1003.1-2001,  Section  8.2,
              Internationalization Variables for the precedence of internationalization variables
              used to determine the values of locale categories.)

       LC_ALL If set to  a  non-empty  string  value,  override  the  values  of  all  the  other
              internationalization variables.

              Determine  the  locale for the interpretation of sequences of bytes of text data as
              characters (for  example,  single-byte  as  opposed  to  multi-byte  characters  in
              arguments and input files).

              Determine  the  locale  that  should  be  used to affect the format and contents of
              diagnostic messages written to standard error.

              Determine the location of message catalogs for the processing of LC_MESSAGES .




       The designated portion of the input file shall be written to standard output.


       The standard error shall be used only for diagnostic messages.






       The following exit values shall be returned:

        0     Successful completion.

       >0     An error occurred.



       The following sections are informative.


       The -c option should be used with caution when the input is a text file containing  multi-
       byte characters; it may produce output that does not start on a character boundary.

       Although  the  input  file to tail can be any type, the results might not be what would be
       expected on some character special device files or on file  types  not  described  by  the
       System    Interfaces    volume    of    IEEE Std 1003.1-2001.   Since   this   volume   of
       IEEE Std 1003.1-2001 does not specify the block size used when doing input, tail need  not
       read all of the data from devices that only perform block transfers.


       The  -f  option  can be used to monitor the growth of a file that is being written by some
       other process. For example, the command:

              tail -f fred

       prints the last ten lines of the file fred, followed by any lines  that  are  appended  to
       fred between the time tail is initiated and killed. As another example, the command:

              tail -f -c 15 fred

       prints the last 15 bytes of the file fred, followed by any bytes that are appended to fred
       between the time tail is initiated and killed.


       This version of tail was created to allow conformance to the  Utility  Syntax  Guidelines.
       The historical -b option was omitted because of the general non-portability of block-sized
       units of text.  The  -c  option  historically  meant  "characters",  but  this  volume  of
       IEEE Std 1003.1-2001  indicates  that  it  means  "bytes".  This  was  selected  to  allow
       reasonable implementations when multi-byte characters are possible; it was not named -b to
       avoid confusion with the historical -b.

       The  origin  of  counting  both  lines  and bytes is 1, matching all widespread historical

       The restriction on the internal buffer is a compromise between  the  historical  System  V
       implementation of 4096 bytes and the BSD 32768 bytes.

       The -f option has been implemented as a loop that sleeps for 1 second and copies any bytes
       that are available. This is sufficient, but if more efficient methods of determining  when
       new data are available are developed, implementations are encouraged to use them.

       Historical  documentation indicates that tail ignores the -f option if the input file is a
       pipe (pipe and FIFO on systems that support FIFOs). On BSD-based systems,  this  has  been
       true;  on  System V-based systems, this was true when input was taken from standard input,
       but it did not ignore the -f flag if a FIFO was named as the file operand.  Since  the  -f
       option  is  not  useful  on  pipes and all historical implementations ignore -f if no file
       operand is specified and standard input is a pipe,  this  volume  of  IEEE Std 1003.1-2001
       requires  this  behavior. However, since the -f option is useful on a FIFO, this volume of
       IEEE Std 1003.1-2001 also requires that if standard input is a FIFO or a  FIFO  is  named,
       the  -f  option  shall not be ignored. Although historical behavior does not ignore the -f
       option for other file types, this is unspecified so that implementations  are  allowed  to
       ignore the -f option if it is known that the file cannot be extended.

       This  was  changed  to  the current form based on comments noting that -c was almost never
       used without specifying a number and that there was no need to specify -l if -n number was






       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1, 2003 Edition, Standard for Information Technology  --  Portable  Operating  System
       Interface  (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by
       the Institute of Electrical and Electronics Engineers, Inc and  The  Open  Group.  In  the
       event  of  any  discrepancy  between this version and the original IEEE and The Open Group
       Standard, the original IEEE and The Open Group  Standard  is  the  referee  document.  The
       original Standard can be obtained online at .