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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?

____________________________________________________________________________________________________________

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/rfc195_.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 explanations 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) nor-mally normally
                     mally 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 transfor-mation. transformation.
                     mation.

                     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 trans-form transform
                     form 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 command 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 command 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 imme-diately immediately
       diately takes data from either its commandline 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  ver-sion version
       sion  7.6  was  current as this and earlier versions have trouble to deal with \0 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)