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OpenSolaris 2009.06 - man page for unpack (opensolaris section 1)

pack(1) 				  User Commands 				  pack(1)

       pack, pcat, unpack - compress and expand files

       pack [-f/] [-] file...

       pcat file...

       unpack [-/] file...

       The pack command attempts to store the specified files in a compressed form. Wherever pos-
       sible (and useful), each input file file is replaced by a packed file file.z with the same
       access  modes,  access and modified dates, and owner as those of file. If pack is success-
       ful, file is removed.

       The amount of compression obtained depends on the size of the input file and the character
       frequency  distribution.  Because a decoding tree forms the first part of each .z file, it
       is usually not worthwhile to pack files smaller than three blocks,  unless  the	character
       frequency distribution is very skewed, which can occur with printer plots or pictures.

       Typically,  text  files	are reduced to 60-75% of their original size. Load modules, which
       use a larger character set and have a more uniform distribution of characters, show little
       compression, the packed versions being about 90% of the original size.

       The  pack  utility returns a value that is the number of files that it failed to compress.
       If that number exceeds 255, 255 is returned.

       No packing occurs if:

	   o	  the file appears to be already packed

	   o	  the file name is too long to add the .z suffix

	   o	  the file has links

	   o	  the file is a directory

	   o	  the file cannot be opened

	   o	  the file is empty

	   o	  no disk storage blocks are saved by packing

	   o	  a file called file.z already exists

	   o	  the .z file cannot be created

	   o	  an I/O error occurred during processing.

       The last segment of the file name must be short enough to allow	space  for  the  appended
       .zextension. Directories cannot be compressed.

       The  pcat  command  does for packed files what cat(1) does for ordinary files, except that
       pcat cannot be used as a filter. The specified files are unpacked and written to the stan-
       dard output.

       pcat returns the number of files it was unable to unpack. Failure can occur if:

	   o	  the file cannot be opened;

	   o	  the file does not appear to be the output of pack.

       The  unpack command expands files created by pack. For each file specified in the command,
       a search is made for a file called file.z (or just file, if file ends in .z). If this file
       appears	to be a packed file, it is replaced by its expanded version. The new file has the
       .z suffix stripped from its name, and has the same access modes, access	and  modification
       dates, and owner as those of the packed file.

       unpack  returns	a  value that is the number of files it was unable to unpack. Failure can
       occur for the same reasons that it can in pcat, as well as for the following:

	   o	  a file with the unpacked name already exists;

	   o	  the unpacked file cannot be created.

       The following options are supported by pack:

       -f    Forces packing of file. This is useful for causing an entire directory to be  packed
	     even  if  some  of  the  files do not benefit. Packed files can be restored to their
	     original form using unpack or pcat.

       The following options are supported by pack and unpack:

       -/    When packing or unpacking, copies any ACL and extended system attributes  associated
	     with  the	source	file  to the target file. If an ACL or extended system attributes
	     cannot be copied, the original file is retained, a diagnostic message is written  to
	     stderr, and the final exit status is non-zero.

       The following operands are supported:

       file    A  path name of a file to be packed, unpacked, or pcated; file can include or omit
	       the .z suffix.

       -       pack uses Huffman (minimum redundancy) codes on a byte-by-byte  basis.  If  the	-
	       argument  is  used,  an	internal flag is set that causes the number of times each
	       byte is used, its relative frequency, and the code for the byte to be  printed  on
	       the  standard  output.  Additional  occurrences	of  - in place of file causes the
	       internal flag to be set and reset.

       See largefile(5) for the description of the  behavior  of  pack,  pcat,	and  unpack  when
       encountering files greater than or equal to 2 Gbyte ( 2^31 bytes).

       Example 1 Viewing a Packed File

       To view a packed file named file.z use:

       example% pcat file.z

       or just:

       example% pcat file

       Example 2 Making and Unpacked Copy:

       To  make  an  unpacked  copy,  say  nnn, of a packed file named file.z (without destroying
       file.z) use the command:

       example% pcat file >nnn

       See environ(5) for descriptions of the following environment  variables	that  affect  the
       execution of pack, pcat, and unpack: LC_CTYPE, LC_MESSAGES, and NLSPATH.

       The following exit values are returned:

       0     Successful completion.

       >0    An  error	occurred.  The	number	of  files  the	command  failed to pack/unpack is
	     returned. If the number of failures exceeds 255, then 255 is returned.

       See attributes(5) for descriptions of the following attributes:

       |Availability		     |SUNWesu			   |
       |CSI			     |Enabled			   |

       cat(1), compress(1), zcat(1), fgetattr(3C), fsetattr(3C)attributes(5), environ(5),  large-

SunOS 5.11				   13 Mar 2008					  pack(1)

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