base64(n)                                                            base64(n)



NAME
       base64 - Encoding "base64"

SYNOPSIS
       package require Tcl  ??8.2??

       package require Trf  ??2.1p2??

       base64 ?options...? ?data?


DESCRIPTION
       The  command  base64  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 three bytes  into  a  block  of
       four  bytes,  each of which is printable, i.e. 7bit ASCI. This implies
       that the result is valid UTF-8 too.  The command uses  essentially  the
       same  algorithm  as  for  uuencode, except for a different mapping from
       6-bit fragments to printable bytes.


       base64 ?options...? ?data?

              -mode encodedecode
                     This option has to be present and is always understood by
                     the encoding.

                     For immediate mode the argument value specifies the oper-
                     ation to use.  For an attached encoding it specifies  the
                     operation  to use for writing. Reading will automatically
                     use the reverse operation.  See section IMEDIATE  versus
                     ATACHED for explanations of these two terms.

                     Beyond the argument values listed above all unique abbre-
                     viations are recognized too.

                     Encode converts from arbitrary (most likely binary)  data
                     into   the  described  representation,  decode  does  the
                     reverse .

              -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 IMEDIATE ver-
                     sus ATACHED.

                     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  IMEDIATE  versus
                     ATACHED.

              -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.

NOTES
       [1]    The encoding is equivalent to PGP's ASCI  armor  and  was  also
              accepted  as  one  of  the  MIME  encodings for encapsulation of
              binary    data.     See    RFC     2045     (http://www.rfc-edi-
              tor.org/rfc/rfc2045.txt)  for  details  and the specification of
              this encoding.

       [2]    The encoding buffers 2 bytes.

IMEDIATE versus ATACHED
       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 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 -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 out-
       put.

SEE ALSO
       ascii85, base64, bin, hex, oct, otpwords, quoted-printable, trf-intro,
       uuencode

KEYWORDS
       ascii armor, base64, encoding, mime, pgp, rfc 2045, uuencode

COPYRIGHT
       Copyright (c) 1996-2003, Andreas Kupries 



Trf transformer commands             2.1p2                           base64(n)