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truncate  -  truncate or extend the length of files truncate [-c]
-s  [+|-]size[K|k|M|m|G|g]  file ...  truncate  [-c]   -r   rfile
file ...  The truncate utility adjusts the length of each regular
file given on the command-line.

The following options are available:
-c      Do not create files if they do not exist.   The  truncate
        utility  does  not  treat  this  as  an  error.  No error
        messages  are  displayed  and  the  exit  value  is   not
        affected.
-r rfile
        Truncate files to the length of the file rfile.
-s [+|-]size[K|k|M|m|G|g]
        If  the  size  argument  is  preceded by a plus sign (+),
        files will be extended by this number of bytes.   If  the
        size  argument  is  preceded  by a dash (-), file lengths
        will be reduced by no more than this number of bytes,  to
        a  minimum  length  of  zero  bytes.  Otherwise, the size
        argument specifies an absolute length to which all  files
        should be extended or reduced as appropriate.

        The  size  argument may be suffixed with one of K, M or G
        (either upper or lower case) to indicate  a  multiple  of
        Kilobytes, Megabytes or Gigabytes respectively.

Exactly one of the -r and -s options must be specified.

If  a file is made smaller, its extra data is lost.  If a file is
made larger, it will be extended as if by writing bytes with  the
value zero.  If the file does not exist, it is created unless the
-c option is specified.

Note that, while truncating a file causes space  on  disk  to  be
freed, extending a file does not cause space to be allocated.  To
extend a file and actually allocate the space, it is necessary to
explicitly write data to it, using (for example) the shell's '>>'
redirection syntax, or dd(1).
The utility exits 0 on success, and >0 if an  error  occurs.   If
the  operation  fails  for  an  argument,  truncate  will issue a
diagnostic and continue processing the remaining arguments.   The
truncate  utility  conforms  to no known standards.  The truncate
utility first appeared in FreeBSD 4.2.  The truncate utility  was
written by Sheldon Hearn <sheldonh@starjuice.net>.