Provided by: tcllib_1.19-dfsg-2_all 
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 representing the same
text in an indexed form and returns that dictionary 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.
::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 text strings as the
associated values. The keys represent the line numbers 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 physical 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 canonical representation
of their input text. The commands taking a dictionary 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 following 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.
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 addition 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 deletion 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 precending 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::decodeRcsPatch 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 structures.
A PCL is a list where each element represents a single patch instruction, either an
addition, or a deletion. The elements are lists themselves, where the first item specifies
the command and the remainder represent the arguments of the command.
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 example 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 Trackers
[http://core.tcl.tk/tcllib/reportlist]. Please also report any ideas for enhancements you
may have for either package and/or documentation.
When proposing code changes, please provide unified diffs, i.e the output of diff -u.
Note further that attachments are strongly preferred over inlined patches. Attachments can
be made by going to the Edit form of the ticket immediately after its creation, and then
using the left-most button in the secondary navigation bar.
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>