ascii85(n) ascii85(n)
NAME
ascii85 - Encoding "ascii85"
SYNOPSIS
package require Tcl ?8.2?
package require Trf ?2.1p2?
ascii85 ?options...? ?data?
DESCRIPTION
The command ascii85 is one of several data encodings provided by the package trf. See trf-intro for
an overview of the whole package.
This encoding transforms every block of four bytes into the Ascii85 representation as defined in the
'Postscript Reference Manual' (2nd Edition, section 3.13, page 129).
ascii85 ?options...? ?data?
-mode encode|decode
This option has to be present and is always understood by the encoding.
For immediate mode the argument value specifies the operation to use. For an attached
encoding 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.
Encode converts from arbitrary (most likely binary) data into the described representa-tion, representation,
tion, decode does the reverse .
-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
ascii85, base64, bin, hex, oct, otp_words, quoted-printable, trf-intro, uuencode
KEYWORDS
ascii85, encoding, postscript
COPYRIGHT
Copyright (c) 1996-2003, Andreas Kupries <andreas_kupries@users.sourceforge.net>
Trf transformer commands 2.1p2 ascii85(n)
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