rcs(3tcl) RCS low level utilities rcs(3tcl)
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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
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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. se-
quences 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.
::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 ig-
nores no-ops in the input, in other words the resulting PCL con-
tains only instructions doing something.
::rcs::encodeRcsPatch pcmds
This command provides the complementary operation to ::rcs::de-
codeRcsPatch. It convert a patch comand list (PCL) list as spec-
ified 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 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 in-
put 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.
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 oc-
cur 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.
a This is the instruction for the addition of text. It has two ar-
guments, 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 ar-
guments, 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 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 out-
put 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>
tcllib 2.0.2 rcs(3tcl)