DragonFly On-Line Manual Pages
zip(n) zip(n)
See the file man.macros.
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(n)