tail(1) - NetBSD Manual Pages

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TAIL(1)                 NetBSD General Commands Manual                 TAIL(1)


NAME

     tail -- display the last part of a file


SYNOPSIS

     tail [-f | -F | -r] [-b number | -c number | -n number] [file ...]


DESCRIPTION

     The tail utility displays the contents of file or, by default, its stan-
     dard input, to the standard output.

     The display begins at a byte, line or 512-byte block location in the
     input.  Numbers having a leading plus (``+'') sign are relative to the
     beginning of the input, for example, ``-c +2'' starts the display at the
     second byte of the input.  Numbers having a leading minus (``-'') sign or
     no explicit sign are relative to the end of the input, for example, ``-n
     2'' displays the last two lines of the input.  The default starting loca-
     tion is ``-n 10'', or the last 10 lines of the input.

     The options are as follows:

     -b number
             The location is number 512-byte blocks.

     -c number
             The location is number bytes.

     -f      The -f option causes tail to not stop when end of file is
             reached, but rather to wait for additional data to be appended to
             the input.  The -f option is ignored if the standard input is a
             pipe, but not if it is a FIFO.

     -F      The -F option is the same as the -f option, except that every
             five seconds tail will check to see if the file named on the com-
             mand line has been shortened or moved (it is considered moved if
             the inode or device number changes) and, if so, it will close the
             current file, open the filename given, print out the entire con-
             tents, and continue to wait for more data to be appended.  This
             option is used to follow log files though rotation by
             newsyslog(8) or similar programs.

     -n number
             The location is number lines.

     -r      The -r option causes the input to be displayed in reverse order,
             by line.  Additionally, this option changes the meaning of the
             -b, -c and -n options.  When the -r option is specified, these
             options specify the number of bytes, lines or 512-byte blocks to
             display, instead of the bytes, lines or blocks from the beginning
             or end of the input from which to begin the display.  The default
             for the -r option is to display all of the input.

     If more than a single file is specified, each file is preceded by a
     header consisting of the string ``==> XXX <=='' where ``XXX'' is the name
     of the file.

     The tail utility exits 0 on success, and >0 if an error occurs.


SEE ALSO

     cat(1), head(1), sed(1)


STANDARDS

     The tail utility is expected to be a superset of the IEEE Std 1003.2-1992
     (``POSIX.2'') specification.  In particular, the -b, -r and -F options
     are extensions to that standard.

     The historic command line syntax of tail is supported by this implementa-
     tion.  The only difference between this implementation and historic ver-
     sions of tail, once the command line syntax translation has been done, is
     that the -b, -c and -n options modify the -r option, i.e. ``-r -c 4''
     displays the last 4 characters of the last line of the input, while the
     historic tail (using the historic syntax ``-4cr'') would ignore the -c
     option and display the last 4 lines of the input.


HISTORY

     A tail command appeared in Version 7 AT&T UNIX.


BUGS

     When using the -F option, tail will not detect a file truncation if,
     between the truncation and the next check of the file size, data written
     to the file make it larger than the last known file size.

NetBSD 3.0                       June 6, 1993                       NetBSD 3.0