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.
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.
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>