bionic (3) zip.3trf.gz

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>