NAME

       zip - Data compression "zip"

SYNOPSIS

       package require Tcl  ?8.2?

       package require Trf  ?2.1.3?

       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/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  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) 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 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
       immediately 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 version 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                              2.1.3                                            zip(3trf)