zip(n)																	    zip(n)

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NAME

       zip - Data compression "zip"

SYNOPSIS

       package require Tcl  ?8.2?

       package require Trf  ?2.1.4?

       zip ?options...? ?data?

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DESCRIPTION

       The command zip is one of several data compressions provided by the package trf. See trf-intro for an overview of the whole package.

       The  command  is  based	on  the  deflate compression algorithm as specified in RFC 1951 (http://www.rfc-editor.org/rfc/rfc1951.txt) and as
       implemented by the zlib compression library (http://www.gzip.org/zlib/).  See also RFC 1950 (http://www.rfc-editor.org/rfc/rfc1950.txt)

       zip ?options...? ?data?

	      -mode compress|decompress
		     This option has to be present and is always understood by the compression.

		     For immediate mode the argument value specifies the operation to use.  For an attached compress it specifies the operation to
		     use  for  writing.  Reading will automatically use the reverse operation.	See section IMMEDIATE versus ATTACHED for explana-
		     tions of these two terms.

		     Beyond the argument values listed above all unique abbreviations are recognized too.

		     Compress causes the compression of arbitrary (most likely binary) data. Decompression does the reverse .

	      -level integer
		     Specifies the compression level. Is either the string default or an integer number in the range 1 (minimal compression) to  9
		     (maximal compression).

	      -nowrap boolean
		     If  set  to  true	the  command will not create the zip specific header (See RFC 1950) normally written before the compressed
		     data. The options defaults to false.  It has to be used when writing a gzip emulation in Tcl  as  gzip  creates  a  different
		     header.

	      -attach channel
		     The presence/absence of this option determines the main operation mode of the transformation.

		     If present the transformation will be stacked onto the channel whose handle was given to the option and run in attached mode.
		     More about this in section IMMEDIATE versus ATTACHED.

		     If the option is absent the transformation is used in immediate mode and the options listed below are recognized. More  about
		     this in section IMMEDIATE versus ATTACHED.

	      -in channel
		     This  options is legal if and only if the transformation is used in immediate mode. It provides the handle of the channel the
		     data to transform has to be read from.

		     If the transformation is in immediate mode and this option is absent the data to transform is expected as the  last  argument
		     to the transformation.

	      -out channel
		     This  options is legal if and only if the transformation is used in immediate mode. It provides the handle of the channel the
		     generated transformation result is written to.

		     If the transformation is in immediate mode and this option is absent the generated data is returned as the result of the com-
		     mand itself.

IMMEDIATE VERSUS ATTACHED

       The transformation distinguishes between two main ways of using it. These are the immediate and attached operation modes.

       For the attached mode the option -attach is used to associate the transformation with an existing channel. During the execution of the com-
       mand no transformation is performed, instead the channel is changed in such a way, that from then on all data written to or  read  from	it
       passes through the transformation and is modified by it according to the definition above.  This attachment can be revoked by executing the
       command unstack for the chosen channel. This is the only way to do this at the Tcl level.

       In the second mode, which can be detected by the absence of option -attach, the transformation immediately takes data from either its  com-
       mandline  or  a	channel,  transforms it, and returns the result either as result of the command, or writes it into a channel.  The mode is
       named after the immediate nature of its execution.

       Where the data is taken from, and delivered to, is governed by the presence and absence of the options -in and -out.  It  should  be  noted
       that this ability to immediately read from and/or write to a channel is an historic artifact which was introduced at the beginning of Trf's
       life when Tcl version 7.6 was current as this and earlier versions have trouble to deal with  characters embedded into  either  input	or
       output.

SEE ALSO

       bz2, trf-intro, zip

KEYWORDS

       compression, data compression, decompression, rfc 1950, rfc 1951, rfc 1952, zip

COPYRIGHT

       Copyright (c) 1996-2003, Andreas Kupries <andreas_kupries@users.sourceforge.net>

Trf transformer commands					       2.1.4								    zip(n)