


rcs(n)               RCS low level utilities               rcs(n)


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NAME
       rcs - RCS low level utilities

SYNOPSIS
       package require Tcl  8.4

       package require rcs  ?0.1?

       ::rcs::text2dict text

       ::rcs::dict2text dict

       ::rcs::file2dict filename

       ::rcs::dict2file filename dict

       ::rcs::decodeRcsPatch text

       ::rcs::encodeRcsPatch pcmds

       ::rcs::applyRcsPatch text pcmds

_________________________________________________________________

DESCRIPTION
       The  Revision  Control  System, short RCS, is a set of applications and
       related data formats which allow a system to  persist  the  history  of
       changes  to  a  text.  It, and its relative SCCS are the basis for many
       other such systems, like CVS, etc.

       This package does not implement RCS.

       It only provides a number of low level commands which should be  useful
       in the implementation of any revision management system, namely:

       [1]    The  conversion of texts into and out of a data structures which
              allow the easy  modification  of  such  text  by  patches,  i.e.
              sequences  of  instructions  for  the transformation of one text
              into an other.

       [2]    And the conversion of one particular format for patches, the so-
              called  RCS patches, into and out of data structures which allow
              their easy application to texts.


COMMANDS
       ::rcs::text2dict text
              Converts the argument text into a dictionary containing and rep-
              resenting the same text in an indexed form and returns that dic-
              tionary as its result.  More information about the format of the
              result  can  be  found in section TEXT DICT DATA STRUCTURE. This
              command returns the canonical representation of the input.



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       ::rcs::dict2text dict
              This   command   provides   the   complementary   operation   to
              ::rcs::text2dict. It converts a dictionary in the form described
              in section TEXT DICT DATA STRUCTURE back into a text and returns
              that  text  as its result. The command does accept non-canonical
              representations of the text as its input.

       ::rcs::file2dict filename
              This command is identical to ::rcs::text2dict,  except  that  it
              reads  the text to convert from the file with path filename. The
              file has to exist and must be readable as well.

       ::rcs::dict2file filename dict
              This command is identical to ::rcs::2dict2text, except  that  it
              stores  the  resulting  text in the file with path filename. The
              file is created if it did not exist, and must be  writable.  The
              result of the command is the empty string.

       ::rcs::decodeRcsPatch text
              Converts  the  text  argument into a patch command list (PCL) as
              specified in the section RCS PATCH COMMAND LIST and returns this
              list  as  its  result.   It is assumed that the input text is in
              diff -n format, also known as RCS patch format, as specified  in
              the  section  RCS  PATCH  FORMAT.   Please note that the command
              ignores no-ops in the input, in other words  the  resulting  PCL
              contains only instructions doing something.

       ::rcs::encodeRcsPatch pcmds
              This   command   provides   the   complementary   operation   to
              ::rcs::decodeRcsPatch. It convert a patch comand list (PCL) list
              as  specified  in the section RCS PATCH COMMAND LIST back into a
              text in RCS PATCH FORMAT and returns that text as its result.

              Note that this command and ::rcs::decodeRcsPatch are not exactly
              complementary, as the latter strips no-ops from its input, which
              the encoder cannot put  back  anymore  into  the  generated  RCS
              patch.  In  other  words, the result of a decode/encode step may
              not match the original input at the character level, but it will
              match it at the functional level.

       ::rcs::applyRcsPatch text pcmds
              This  operation  applies  a patch in the form of a PCL to a text
              given in the form of a dictionary and returns the modified text,
              again as dictionary, as its result.

              To  handle  actual  text  use  the commands ::rcs::text2dict (or
              equivalent) and ::rcs::decodeRcsPatch to  transform  the  inputs
              into data structures acceptable to this command. Analogously use
              the command ::rcs::dict2text (or equivalent)  to  transform  the
              result of this command into actuall text as required.


TEXT DICT DATA STRUCTURE
       A  text  dictionary  is a dictionary whose keys are integer numbers and



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       text strings as the associated values. The keys represent the line num-
       bers  of  a  text  and the values the text of that line.  Note that one
       text can have many representations as a dictionary, as the index values
       only have to be properly ordered for reconstruction, their exact values
       do not matter. Similarly the strings may actually span multiple  physi-
       cal lines.

       The text

       Hello World,
       how are you ?
       Fine, and you ?

       for example can be represented by

       {{1 {Hello World,}} {2 {how are you ?}} {3 {Fine, and you ?}}}

       or

       {{5 {Hello World,}} {8 {how are you ?}} {9 {Fine, and you ?}}}

       or

       {{-1 {Hello World,
       how are you ?}} {4 {Fine, and you ?}}}

       The  first dictionary is the canonical representation of the text, with
       line numbers starting at 1, increasing in steps of 1 and without  gaps,
       and each value representing exactly one physical line.

       All the commands creating dictionaries from text will return the canon-
       ical representation of their input text. The commands taking a  dictio-
       nary  and  returning  text  will  generally accept all representations,
       canonical or not.

       The result of applying a patch to a text  dictionary  will  in  general
       cause the dictionary to become non-canonical.

RCS PATCH FORMAT
       A  patch  is  in  general  a series of instructions how to transform an
       input text T into a different text T', and also encoded in text form as
       well.

       The text format for patches understood by this package is a very simple
       one, known under the names RCS patch or diff -n format.

       Patches in this format contain only two  different  commands,  for  the
       deletion of old text, and addition of new text. The replacement of some
       text by a different text is handled as combination of a  deletion  fol-
       lowing by an addition.

       The format is line oriented, with each line containing either a command
       or text data associated with the preceding command.  The first line  of
       a RCS patch is always a command line.



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       The commands are:

       ""     The empty line is a command which does nothing.

       "astart n"
              A  line starting with the character a is a command for the addi-
              tion of text to the output. It is followed by n  lines  of  text
              data. When applying the patch the data is added just between the
              lines start and start+1. The same effect is had by appending the
              data  to  the  existing  text on line start. A non-existing line
              start is created.

       "dstart n"
              A line starting with the character d is a command for the  dele-
              tion of text from the output. When applied it deletes n lines of
              text, and the first line deleted is at index start.

       Note that the line indices start always refer  to  the  text  which  is
       transformed as it is in its original state, without taking the precend-
       ing changes into account.

       Note also that the instruction have to be applied  in  the  order  they
       occur  in  the  patch, or in a manner which produces the same result as
       in-order application.

       This is the format of results returned by the command  ::rcs::decodeRc-
       sPatch   and   accepted   by  the  commands  ::rcs::encodeRcsPatch  and
       ::rcs::appplyRcsPatch resp.  Note however that the decoder  will  strip
       no-op  commands,  and the encoder will not generate no-ops, making them
       not fully complementary at the textual level, only  at  the  functional
       level.

       And example of a RCS patch is

       d1 2
       d4 1
       a4 2
       The named is the mother of all things.

       a11 3
       They both may be called deep and profound.
       Deeper and more profound,
       The door of all subtleties!

RCS PATCH COMMAND LIST
       Patch  command lists (sort: PCL's) are the data structures generated by
       patch decoder command and accepted by the patch encoder and  applicator
       commands.  They  represent  RCS  patches in the form of Tcl data struc-
       tures.

       A PCL is a list where each element represents a single  patch  instruc-
       tion,  either  an addition, or a deletion. The elements are lists them-
       selves, where the first item specifies the command  and  the  remainder
       represent the arguments of the command.



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       a      This  is  the  instruction  for the addition of text. It has two
              arguments, the index of the line where to add the text, and  the
              text to add, in this order.

       d      This  is  the  instruction  for the deletion of text. It has two
              arguments, the index of the line where to start  deleting  text,
              and the number of lines to delete, in this order.


       This  is  the format returned by the patch decoder command and accepted
       as input by the patch encoder and applicator commands.

       An example for a patch command is shown below, it represents the  exam-
       ple RCS patch found in section RCS PATCH FORMAT.

       {{d 1 2} {d 4 1} {a 4 {The named is the mother of all things.

       }} {a 11 {They both may be called deep and profound.
       Deeper and more profound,
       The door of all subtleties!}}}

BUGS, IDEAS, FEEDBACK
       This  document,  and the package it describes, will undoubtedly contain
       bugs and other problems.  Please report such in the category rcs of the
       Tcllib  SF  Trackers  [http://sourceforge.net/tracker/?group_id=12883].
       Please also report any ideas for enhancements you may have  for  either
       package and/or documentation.

SEE ALSO
       struct, textutil

KEYWORDS
       CVS,  RCS,  RCS patch, SCCS, diff -n format, patching, text conversion,
       text differences

CATEGORY
       Text processing

COPYRIGHT
       Copyright (c) 2005, Andreas Kupries <andreas_kupries@users.sourceforge.net>
       Copyright (c) 2005, Colin McCormack <coldstore@users.sourceforge.net>
















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