Provided by: rcs_5.9.4-5_amd64 bug

NAME

       rcsfile - RCS file format

DESCRIPTION

       An RCS file's contents are described by the grammar below.

       The  text  is  free  format:  space, backspace, tab, newline, vertical tab, form feed, and
       carriage return (collectively, white  space)  have  no  significance  except  in  strings.
       However,  white  space  cannot  appear within an id, num, or sym, and an RCS file must end
       with a newline.

       Strings are enclosed by @.  If a string contains a  @,  it  must  be  doubled;  otherwise,
       strings can contain arbitrary binary data.

       The  meta syntax uses the following conventions: `|' (bar) separates alternatives; `{' and
       `}' enclose optional phrases; `{' and `}*' enclose phrases that can be  repeated  zero  or
       more  times;  `{'  and  '}+'  enclose  phrases  that  must appear at least once and can be
       repeated; Terminal symbols are in boldface; nonterminal symbols are in italics.

       rcstext   ::=  admin {delta}* desc {deltatext}*

       admin     ::=  head       {num};
                      { branch   {num}; }
                      access     {id}*;
                      symbols    {sym : num}*;
                      locks      {id : num}*;  {strict  ;}
                      { integrity{intstring}; }
                      { comment  {string}; }
                      { expand   {string}; }

       delta     ::=  num
                      date       num;
                      author     id;
                      state      {id};
                      branches   {num}*;
                      next       {num};
                      { commitid sym; }

       desc      ::=  desc       string

       deltatext ::=  num
                      log        string
                      text       string

       num       ::=  {digit | .}+

       digit     ::=  0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9

       id        ::=  {idchar | .}+

       sym       ::=  {idchar}+

       idchar    ::=  any visible graphic character except special

       special   ::=  $ | , | . | : | ; | @

       string    ::=  @{any character, with @ doubled}*@

       word      ::=  id | num | string | :

       intchar   ::=  any character, except @

       thirdp    ::=  ^L {intchar}*

       intstring ::=  @ {intchar}* {thirdp}* @

       In releases prior to 5.8 (2011-08-30), the grammar included the newphrase  production  and
       used  it in the admin, delta and deltatext productions.  This allowed third-party programs
       to interoperate with RCS by storing opaque (to RCS) data in the file.  As of 5.8,  in  the
       name  of progress (towards more systematic file integrity support), the only area reserved
       for third-party interop is in the (string) value  of  the  integrity  field,  specifically
       after  the  first  ^L  (formfeed).   A  further restriction (for all programs) is that the
       integrity value must not contain @.

       Identifiers are case sensitive.  Keywords are in lower case only.  The  sets  of  keywords
       and  identifiers  can  overlap.   In  most  environments RCS uses the ISO 8859/1 encoding:
       visible graphic characters are codes 041-176 and 240-377, and white space  characters  are
       codes 010-015 and 040.

       Dates,  which  appear after the date keyword, are of the form Y.mm.dd.hh.mm.ss, where Y is
       the year, mm the month (01-12), dd the day (01-31), hh the hour  (00-23),  mm  the  minute
       (00-59),  and  ss the second (00-60).  Y contains just the last two digits of the year for
       years from 1900 through 1999, and all the digits  of  years  thereafter.   Dates  use  the
       Gregorian calendar; times use UTC.

       The delta nodes form a tree.  All nodes whose numbers consist of a single pair (e.g., 2.3,
       2.1, 1.3, etc.)  are on the trunk, and are linked through  the  next  field  in  order  of
       decreasing  numbers.  The head field in the admin node points to the head of that sequence
       (i.e., contains the highest pair).  The branch  node  in  the  admin  node  indicates  the
       default branch (or revision) for most RCS operations.  If empty, the default branch is the
       highest branch on the trunk.

       All delta nodes whose numbers consist of 2n fields (n≥2) (e.g.,  3.1.1.1,  2.1.2.2,  etc.)
       are  linked as follows.  All nodes whose first 2n-1 number fields are identical are linked
       through the next field in order of increasing numbers.  For each such sequence, the  delta
       node  whose  number  is  identical  to  the first 2n-2 number fields of the deltas on that
       sequence is called the branchpoint.  The branches field of a node contains a list  of  the
       numbers  of  the first nodes of all sequences for which it is a branchpoint.  This list is
       ordered in increasing numbers.

       The following diagram shows an example of an RCS file's organization.

                                  Head
                                    |
                                    |
                                    v                        / \
                                ---------                   /   \
          / \          / \      |       |      / \         /     \
         /   \        /   \     |  2.1  |     /   \       /       \
        /     \      /     \    |       |    /     \     /         \
       /1.2.1.3\    /1.3.1.1\   |       |   /1.2.2.2\   /1.2.2.1.1.1\
       ---------    ---------   ---------   ---------   -------------
           ^            ^           |           ^             ^
           |            |           |           |             |
           |            |           v           |             |
          / \           |       ---------      / \            |
         /   \          |       \  1.3  /     /   \           |
        /     \         ---------\     /     /     \-----------
       /1.2.1.1\      1.3.1       \   /     /1.2.2.1\     1.2.2.1.1
       ---------                   \ /      ---------
           ^                        |           ^
           |                        |           |
           |                        v           |
           |                    ---------       |
           |                    \  1.2  /       |
           ----------------------\     /---------
         1.2.1                    \   /       1.2.2
                                   \ /
                                    |
                                    |
                                    v
                                ---------
                                \  1.1  /
                                 \     /
                                  \   /
                                   \ /

IDENTIFICATION

       Author: Walter F. Tichy.
       Manual Page Revision: 5.9.4; Release Date: 2019-02-10.
       Copyright © 2010-2015 Thien-Thi Nguyen.
       Copyright © 1990, 1991, 1992, 1993, 1994, 1995 Paul Eggert.
       Copyright © 1982, 1988, 1989 Walter F. Tichy.

SEE ALSO

       ci(1), co(1), ident(1), rcs(1), rcsclean(1), rcsdiff(1), rcsmerge(1), rlog(1).

       Walter F. Tichy, RCS--A System for Version Control, Software--Practice & Experience 15,  7
       (July 1985), 637-654.

       The  full documentation for RCS is maintained as a Texinfo manual.  If the info(1) and RCS
       programs are properly installed at your site, the command

              info rcs

       should give you access to the complete manual.  Additionally, the RCS homepage:

              http://www.gnu.org/software/rcs/

       has news and links to the latest release, development site, etc.