Manual Pages for UNIX Darwin command on man bz2

bz2(n) bz2(n)

NAME

bz2 - Data compression "bz2"

SYNOPSIS

package require TTccll ??88..22?? package require TTrrff ??22..11pp22?? bbzz22 ?options...? ?data?

DESCRIPTION

The command bbzz22 is one of several data compressions provided by the

package ttrrff. See ttrrff-iinnttrroo for an overview of the whole package.

The command is based on the Burroughs-Wheeler transformation as imple-

mented by the bzip2 compression library (http://sources.red-

hat.com/bzip2/). bbzz22 ?options...? ?data?

-mmooddee ccoommpprreessss|ddeeccoommpprreessss

This option has to be present and is always understood by the compression.

For immediate mode the argument value specifies the oper-

ation to use. For an attached compress it specifies the operation to use for writing. Reading will automatically use the reverse operation. See section IIMMMMEEDDIIAATTEE vveerrssuuss AATTTTAACCHHEEDD for explanations of these two terms.

Beyond the argument values listed above all unique abbre-

viations are recognized too. CCoommpprreessss causes the compression of arbitrary (most likely binary) data. DDeeccoommpprreessssiioonn does the reverse .

-lleevveell integer

Specifies the compression level. Is either the string

ddeeffaauulltt or an integer number in the range 11 (minimal com-

pression) to 99 (maximal compression).

-aattttaacchh 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 IIMMMMEEDDIIAATTEE vveerr-

ssuuss AATTTTAACCHHEEDD. If the option is absent the transformation is used in

immediate mode and the options listed below are recog-

nized. More about this in section IIMMMMEEDDIIAATTEE vveerrssuuss AATTTTAACCHHEEDD.

-iinn 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.

-oouutt 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. IIMMMMEEDDIIAATTEE vveerrssuuss AATTTTAACCHHEEDD The transformation distinguishes between two main ways of using it. These are the immediate and attached operation modes.

For the attached mode the option -aattttaacchh 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 uunnssttaacckk 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

-aattttaacchh, 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 -iinn and -oouutt. 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 out-

put.

bz2, trf-intro, zip

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